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Living species retain memories of their evolutionary history in their DNA, and that evolutionary history commonly reflects distinct geological events, such as mountain building and glaciation. We synthesize previously documented genetic data for freshwater fishes and a wide range of upland insect and bird species to document the Pliocene and early Pleistocene topographic and glacial history of the Southern Alps of New Zealand. Genetic data for fish suggest that a long, linear mountain chain was established in the Pliocene. At that time, the mountain chain had a tectonically constructed narrow topographic neck in the middle, with wider uplift zones at either end. Separation of populations of upland insects and birds into faunal zones at the wider ends was caused by a major glacial advance at the narrow tectonic neck at 2 ± 0.5 Ma. The composite biological memory constrains the relative timing of uplift of the Southern Alps as a linear mountain chain, with subsequent imposition of temperate glaciation during Pliocene-Pleistocene cooling in the Southern Hemisphere.

The obliquity of the arc-continent collision in Taiwan is thought to have produced a southward-propagating orogenic system starting as early as 8 Ma. We combine 62 new zircon fission-track ages with timing of rapid subsidence in the foreland basin to identify the timing of the onset of exhumation and orogenesis. The oldest completely reset zircon fission-track ages and the onset of rapid tectonic subsidence in both the northern and southern parts of the foreland basin are ca. 5–6 Ma. We propose that north-south rifting in the South China Sea created a north-trending continental margin before the collision rather than the commonly assumed northeast-trending margin. Consequently, both this north-trending continental margin and the Luzon arc of the Philippine Sea plate were subparallel, resulting in an initial collision that was simultaneous along strike.

The analysis of new and published Hf and Nd isotopic data of late Cenozoic Andean arc igneous rocks from central Chile, coupled with our improved knowledge of orogenic processes in the region, reveals a tight link between major magmatic isotopic shifts and different Andean basement domains and timing of the main uplifting event. Oligocene–Miocene magmas from the Western Principal Cordillera show a nearly constant and juvenile composition (e HfI : +5 to +10; e NdI : +2 to +7), while those from the Eastern Principal Cordillera, formed since early late Miocene, are variably more enriched (e HfI : −4 to +4; e NdI : 0 to +3). Post–4.8 Ma magmas from both belts share an enriched signature (e NdI : −2 to +2) reflecting source contamination from east to west, contrary to the eastward subduction direction, in a process that occurred toward the end of the main Andean uplifting event. This results from the deep western basement underthrusting the orogen, and thus accounts for the westward propagation of the eastern enriched isotopic signatures approximately coeval with thickening and uplifting events. The observed patterns highlight the strong control exerted by the continental lithosphere on the composition of arc magmas over deep controls from the subduction-modified asthenospheric mantle. Moreover, they dynamically represent both (1) the hybridization affecting magmas ascending from the mantle in a heterogeneous continental lithosphere, and (2) the evolution of such lithosphere resulting from the thermal weakening and mass transfer processes occurring underneath cordilleran arcs during mountain building.

The Tien Shan in Central Asia are the pre-eminent example of intraplate mountain building, and are typically considered an indirect result of the India-Eurasia collision, via the northward indentation of the relatively strong Precambrian lithosphere of the Tarim plate into the relatively weak Paleozoic lithosphere of the Tien Shan region. This hypothesis fails to fully explain the concentration of Tien Shan mountain building along a Tibet-parallel axis, located 500–700 km from Tibet, and also fails to explain the close synchronization of Tien Shan mountain-building events with mountain building in Tibet. I suggest that bending stresses from lithospheric flexure in Central Asia exerted a critical influence on the locus and evolution of the Tien Shan. Models of Paleogene to Middle Miocene flexure indicate that the growth of northeast Tibet may have superimposed a strong bending stress field on the regional stress field. The resultant stress field is characterized by strong topography-normal tensile stress in the Tarim Basin, and an ∼15% increase in compressive stress in the vicinity of the Tien Shan. This stress field severely reduces the likelihood of mountain building south of the Tien Shan, and increases the likelihood of mountain building within the Tien Shan. This result suggests that the generation of bending stresses from lithospheric flexure is a viable and important mechanism for the propagation of stress, and hence deformation, into continental interiors.

The time and rate of Tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change. Models predict that the uplift of the north Tibetan Plateau (NTP) occurred later than uplift of the south and central Tibetan Plateau; uplift of the NTP is believed to have initiated the aridity in the interior of Asia, and to have critically affected the evolution of Asian monsoon and, ultimately, global climate. The history of NTP uplift has remained uncertain, however; scenarios range from Early Miocene to the past million years. This work provides new evidence by relating the Nd isotopic evolution of Asian dust to NTP uplift. The sources of the Asian dust are located in the arid lands between the NTP and the Central Asia orogen. Mass balance calculations indicate that the decreasing e Nd values, from −8.2 to −10.4 for Pacific dust since 15 Ma, reflects increasing relative contribution of NTP materials (40% to 70%) to the dust source. As paleoelevation in the Central Asia orogen has largely remained constant, the increasing relative NTP detritus contribution is interpreted to reflect the progressive surface uplift of the NTP at a rate of at least 0.12 mm yr −1 since 15 Ma.

The Atlas Mountains of Morocco have received considerable attention in the past decade regarding the lithospheric structure and the uplift mechanisms of this structurally simple mountain belt. Miller and Becker (2014) have recently added to the discussion with new results from receiver functions and shear-wave splitting analysis. These results confirm the mantle upwelling hypothesis for the Atlas uplift that was postulated 10 years ago and we now see highlighted in several forums. The relationship between modest tectonic shortening and high topography in the Atlas was first addressed by Teixell et al. (2003). They concluded that crustal thickness is insufficient to account for the observed elevations, and proposed a mantle-driven (upwelling) component of uplift, supported by low seismic velocities in the Atlas mantle reported already by Seber et al. (1996). Subsequent efforts focused on modeling of gravity, the geoid, and topography that indicated a prominent lithospheric thinning, placing the lithosphere-asthenosphere boundary (LAB) at 70–90 km beneath the Atlas Mountains (e.g., Teixell et al., 2005; Zeyen et al., 2005; Missenard et al., 2006; Fullea et al., 2010). New contributions on the basis of active and passive seismology, partly under the Picasso project frame, are on their way (e.g., Bezada et al., 2013; Carbonell et al. 2013; Palomeras et al., 2013; Miller and Becker, 2014). Miller and Becker present a receiver functions profile that also shows a thinned crust and lithosphere beneath the Atlas Mountains. However, the thinned domain is bounded by abrupt steps coinciding with the location of the South Atlas thrust front; the authors propose offsets of 9 km of the Moho and 26 km of the LAB across the boundary thrust fault at Errachidia (Miller and Becker, 2014, their figure 2), arguing for the important role of lithosphericscale discontinuities in the Atlas mountain building. As for the crust, this is intriguing because early refraction studies by Wigger et al. (1992) and a more dense wide-angle survey by Carbonell et al. (2013) failed to detect a crustal step in this position, but especially because there is ample evidence that the South Atlas fault is a low-angle thrust zone (Saint Bezar et al. 1988; Teixell et al., 2003). Moreover, Miller and Becker imply that the same fault discontinuity goes down to offset the LAB, which means that the South Atlas thrust projects vertically to a depth of 90 km. This has doubtful geological sense even assuming that the present-day thrusts derive from the inversion of earlier extensional faults: those would also have a dip, and at a depth of 90 km they would be off the vertical projection of the fault surface exposure. Miller and Becker recognize that previous authors document shallowly dipping thrust faults from outcrop and seismic reflection studies, but they do not further discuss this issue. We are left questioning whether there is an enigmatic geological feature in the Atlas that escapes our understanding, or an issue of seismic data resolution. Miller and Becker compare the detected position of the LAB with a modeled position on the basis of the residual topography and on the assumption of isostasy, resulting in a large discrepancy, as the modeled LAB is even shallower than the actual base of the crust. This indicates a strong contribution of dynamic topography due to active mantle upwelling. We do not question the validity of dynamic topography for the Atlas, but we miss a discussion of the earlier potential field models which, on the basis of isostatic equilibrium, fitted the residual topography and the geoid with a greater lithospheric thickness, which would be in accord with the new receiver function results (see references above). Finally, we wish to conclude with a formal comment on the referencing to earlier work in the Atlas. Miller and Becker report a small orogenic shortening (15%–25%) inconsistent with Airy isostatic support and cite four papers, but none of them resulting in these small values of shortening nor do they address relationships between shortening and topography. Fullea et al. (2010) are not the primary reference for the distribution of Quaternary basalts, Frizon de Lamotte et al. (2009) do not provide cross sections to demonstrate shallowly dipping thrust faults, Sebrier et al. (2006) do not provide regional tomography models, and Beauchamp et al. (1999) do not suggest a mantle thermal anomaly as the source of volcanism in the Middle Atlas. Although these citations by Miller and Becker do not alter the main point of their paper, we wish to raise a word of caution for the persistence of incorrect citations.

The recent dramatic increase in seismic anisotropy and surface global positioning system (GPS) data for central Asia permits a comprehensive examination of the mantle’s role in mountain building. A joint analysis of 178 shear-wave-splitting and ~2000 GPS observations using a new technique reveals that the crust and lithospheric mantle deform coherently, arguing for crust-mantle mechanical coupling during deformation. The observed spatial variations in anisotropy refl ect the large-scale pattern of lithospheric deformation, as well as a change in deformational style from simple shear on the Tibetan Plateau transitioning to pure shear in surrounding regions.

Studies across a broad range of drainage basins have established a positive correlation between mean slope gradient and denudation rates. It has been suggested, however, that this relationship breaks down for catchments where slopes are at their threshold angle of stability because, in such cases, denudation is controlled by the rate of tectonic uplift through the rate of channel incision and frequency of slope failure. This mechanism is evaluated for the San Bernardino Mountains, California, a nascent range that incorporates both threshold hillslopes and remnants of pre-uplift topography. Concentrations of in situ–produced cosmogenic 10 Be in alluvial sediments are used to quantify catchment-wide denudation rates and show a broadly linear relationship with mean slope gradient up to ∼30°: above this value denudation rates vary substantially for similar mean slope gradients. We propose that this decoupling in the slope gradient–denudation rate relationship marks the emergence of threshold topography and coincides with the transition from transport-limited to detachment-limited denudation. The survival in the San Bernardino Mountains of surfaces formed prior to uplift provides information on the topographic evolution of the range, in particular the transition from slope-gradient–dependent rates of denudation to a regime where denudation rates are controlled by rates of tectonic uplift. This type of transition may represent a general model for the denudational response to orogenic uplift and topographic evolution during the early stages of mountain building.

Although detrital zircon has proven to be a powerful tool for determining provenance, past work has focused primarily on delimiting regional source terranes. Here we explore the limits of spatial resolution and stratigraphic sensitivity of detrital zircon in ascertaining provenance, and we demonstrate its ability to detect source changes for terranes separated by only a few tens of kilometers. For such an analysis to succeed for a given mountain, discrete intrarange source terranes must have unique U/Pb zircon age signatures and sediments eroded from the range must have well-defi ned depositional ages. Here we use ~1400 single-grain U/Pb zircon ages from northeastern Tibet to identify and analyze an area that satisfi es these conditions. This analysis shows that the edges of intermontane basins are stratigraphically sensitive to discrete, punctuated changes in local source terranes. By tracking eroding rock units chronologically through the stratigraphic record, this sensitivity permits the detection of the differential rock uplift and progressive erosion that began ca. 8 Ma in the Laji Shan, a 10‐25-km-wide range in northeastern Tibet with a unique U/Pb age signature.

A synthesis of transpressive mountain building, as evidenced by rock uplift and topography along the entire San Andreas fault, reveals a complex crustal response to oblique plate motion. Convergent deformation increases toward the fault but does not correlate with the angle of plate-motion obliquity. The shortening estimated from rock uplift is also insufficient to account for the fault-normal motion based on relative plate velocity. This suggests that near-field convergence is influenced by local structural complexity and is not purely driven by regional transpression, and that the fault-normal component of plate motion is partly accommodated elsewhere. Heterogeneity in deformation and degree of slip partitioning highlight the importance of other factors in shaping transpressive continental deformation, including surface processes, material anisotropy, and strain weakening.

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that link remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear, as are the main factors controlling long-term changes in plate motion. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we present for the first time a model that explicitly links global mantle convection and lithosphere models to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates over the past 10 m.y., we demonstrate that surface topography generated at convergent margins is a key factor controlling the long-term evolution of plate motion. Specifically, the topographic load of large mountain belts and plateaus consumes a significant amount of the driving force available for plate tectonics by increasing frictional forces between downgoing and overriding plates.

Analysis of force and torque balance on the Salton block, Southern California, yields estimates of time-averaged shear stress acting on the bounding faults and the base of the crust. Averaged over a depth of 30 km, the San Andreas and San Jacinto faults sustain time-averaged shear stress of ;21-35 and 24-43 MPa, respectively. This implies that tectonic shear stress at seismogenic depths is greater than a typical 1-10 MPa earthquake stress drop and, with a corresponding effective friction coefficient of 0.10-0.21, lower than that predicted by laboratory experiments. Basal stress of 3-14 MPa also is required to drive the Salton block into the Transverse Ranges. Thus, the forces driving mountain building, basin formation, and the generation of earthquakes south of the Transverse Ranges in Southern California stem from stresses transmitted laterally across weak faults and from below.

An emerging paradigm that equates glaciers to ''buzz saws'' of exceptional erosional efficiency has been strengthened by short- term (,10 2 yr) sediment yields from southern Alaska. New low- temperature cooling ages from this area, the glaciated Chugach- St. Elias Mountains, constrain long-term (10 6 yr) exhumation rates. Vertically averaged exhumation rates reach ;3 mm/yr, but are an order of magnitude lower than rates based on short-term sediment yields. Whereas these exhumation rates are not exceptional for oro- genic belts, denudation patterns are strongly correlated with the distribution of glaciers, and erosion appears to keep pace with con- vergence and uplift. These findings imply a coupling between gla- cially dominated erosion and tectonics.

Alpine glacial erosion may strongly influence mountain building through erosionally driven rock uplift and relief production. In this paper I use a three-dimensional model for the flexural-isostatic response of the lithosphere to estimate the potential for late Cenozoic erosionally driven rock uplift in the western United States. Specifically, I present a map of the ratio of erosionally driven rock uplift to glacial erosion for this region. This ratio depends on the magnitude of the flexural bending stresses that act to limit differential uplift. The map is created by constraining the extent of Pliocene–Quaternary alpine glacial erosion in the western United States and solving the three-dimensional flexure equation for the resulting lithospheric deflection. The map indicates that the magnitude of erosionally driven uplift depends sensitively on the size of the glaciated range and the presence of nearby glaciated ranges. As a result, regional-scale patterns must be considered in order to correctly estimate local amounts of erosionally driven rock uplift. The ranges in the western United States with the greatest ratios of uplift to erosion are the San Juan Mountains and the Yellowstone Plateau–Absaroka Range, because these are extensively glaciated and have glaciated ranges nearby. In contrast, the Wind River Range and Sierra Nevada have ratios of uplift to erosion that are only half as large. These results identify which ranges likely underwent the greatest erosionally driven uplift and relief production and provide a widely applicable technique for modeling the flexural-isostatic response to loading and unloading in three dimensions.

To examine the influence of mountain uplift on the long-term carbon cycle, we used geochemical, hydrologic, and suspended-load data for 12 streams draining the New Zealand Southern Alps to quantify rates of erosion, weathering, and atmospheric CO 2 consumption. Rapid uplift in the western Southern Alps elevates mechanical erosion rates by a factor of ∼13 relative to those on the tectonically stable eastern side [125 × 10 8 vs. 9.4 × 10 8 g/(km 2 ·yr), respectively]. Similarly, the average chemical weathering rate is ∼5 times higher on the western compared to eastern side of the mountain range [9.8 × 10 7 vs. 2.0 × 10 7 g/(km 2 ·yr), respectively]. However, because the proportion of stream-water Ca 2+ and Mg 2+ from carbonate weathering increases as the rate of mechanical erosion increases, the long-term atmospheric CO 2 consumption rate on the western side is ∼2 times higher than that on the eastern side [14 × 10 4 vs. 6.9 × 10 4 mol/(km 2 ·yr), respectively] and only ∼1.5 times higher than the global mean value [∼9 × 10 4 mol/(km 2 ·yr)]. Data for major world rivers (including Himalayan rivers) provide a consistent interpretation regarding the relationship between mechanical erosion intensity and the ratio of silicate to carbonate weathering. Thus, we conclude that mountain building increases atmospheric CO 2 consumption rates by only a factor of ∼2, which is much lower than previous estimates.

Comparisons of newly published cross sections across the Bolivian Andes with existing cross sections through Argentina emphasize significant along-strike changes in crustal shortening. A sharp decrease in the magnitude of crustal shortening from ∼530 km to ∼150 km (north to south) occurs at ∼23°S. A 20–40 m.y. difference in the ages at which deformation was initiated accompanies the abrupt decrease in the magnitude of shortening. Extending the western margin of South America to account for 530 km of shortening in the Bolivian Andes and 150 km of shortening in Argentina produces a central Andean salient that is perpendicular to the Nazca plate shortening direction from 60 to 26 Ma. During this same time interval, the Chilean coast south of 23°S was in an orientation sufficiently oblique to oceanic convergence to allow for predominantly strike-slip offset and backarc extension. Deformation within the Andean mountain chain may be a function of plate convergence where the oblique nature of convergence south of ∼23°S inhibited mountain building, whereas north of ∼23°S, normal convergence to a central Andean salient facilitated contractional deformation. The magnitude of deformation north of ∼23°S is a consequence of both plate-convergence direction, providing a longer period of contractional deformation (from ca. 70 Ma to the present), and a thick Phanerozoic sedimentary package that permitted large magnitudes of thin-skinned deformation. Significant along-strike changes in the shape of the South American margin—allowing for convergence to change from compression to extension along the strike of the orogen—may help explain the dramatic differences in timing, amount, and style of deformation in the Andes.

Earthquakes recorded by a dense seismic array at Nanga Parbat, Pakistan, provide new insight into synorogenic metamorphism and mass flow during mountain building. Micro- seismicity beneath the massif drops off sharply with depth and defines a shallow transition between brittle failure and ductile flow. The base of seismicity bows upward, mapping a thermal boundary with 3 km of structural relief over a lateral distance of 12 km. Anom- alously low seismic velocities are observed at the core of the massif and extend to depth through the crust. The main locus of seismicity and low velocities correlates with a region of high topography, rapid exhumation, high geothermal gradients, young metamorphic and igneous ages, and crustal fluid flow. We suggest a genetic link between these phenom- ena in which hot rocks, rapidly advected from depth, are pervasively modified at relatively shallow levels in the crust.

Mountains are distributed across the surface of Io, the fiercely tidally heated moon of Jupiter. The large crustal thicknesses implied by their great heights can be reconciled with Io's high heat flow, if most of the heat escapes directly via volcanic eruptions (the heat-pipe model), but the origin of the mountains has remained obscure. Recent images show that many of Io's mountains are tilted blocks undergoing tectonic collapse, and we propose here that the volcanic heat-pipe (and continuous terrain burial) model naturally leads to such unstable topography. That is, burial (1) generates horizontal tensile stresses as the volcanic crustal stack is loaded, (2) creates large horizontal compressive confining stresses as Io's crust subsides (moves to a smaller effective radius), and importantly, (3) allows for potentially large horizontal compressive thermal stresses as the base of the crust reheats owing to fluctuations in the efficiency of the volcanic heat piping. Faulting associated with these stresses may raise mountain scarps directly or in concert with thermal uplift due to the crustal reheating; continued crustal heating and melting then lead to mountain collapse (all over

The paleorelief of mountain belts can be estimated from the δ 18 O value of authigenic minerals. Development of relief during mountain building often creates lee-side rain shadows in which precipitation is depleted in 18 O and D. The magnitude of this rain-shadow effect is strongly correlated to relief. A compilation of δ 18 O data from surface waters throughout the globe shows a linear relationship between net elevation change and Δδ 18 O ( R 2 = 0.79). Through the use of this relationship, we investigated the timing and magnitude of elevation change in the Southern Alps of New Zealand and the Sierra Nevada of California. The δ 18 O values of kaolinites from New Zealand show an ∼6‰ decrease in the early Pliocene that corresponds to an ∼2 km elevation change in the Southern Alps. The δ 18 O of smectites from the Sierra Nevada show little change since 16 Ma, suggesting that these mountains have been a long-standing topographic feature.

The equivalent elastic thickness (EET) is used to estimate lithospheric strength expressed in response to loading by topography and subsurface loads. The data on EET allow comparisons between different plates and detection of thermal events. In oceans, the EET corresponds to the mechanical “core” of the lithosphere, i.e., a geotherm (400–600 °C). In continents, the EET has no relation to any depth. This has led to doubts in applicability of a unique approach to the continents and oceans, and in the utility of estimates of EET for continents. Rheological data suggest that most rocks are inelastic in the long term (>0.1 m.y.). This requires interpretation of the EET in terms of real rheology. We propose an analytical model that gives rheological interpretation of both the oceanic and continental EET. It also allows estimates of the mechanical thickness of the lithosphere. The EET depends upon three parameters: geotherm age, crustal thickness, and flexural plate curvature. Any one of these values can be estimated if the others are known. Comparisons of model predictions with the observed EET suggest that most continental plates have a weak lower crust, allowing mechanical decoupling between the upper crust and the mantle lithosphere. Such decoupling leads to strong reduction in the EET and thus can be easily detected. Flow of rocks in the weak lower crust may have a significant influence on the temporal evolution of relief (mountain building, erosion). Differences in the mechanical behavior of oceans and continents can be explained by domination of different parameters: geotherm age has a major control in the oceans, whereas in the continents crustal thickness is equally important. Additional local variations of the EET result from weakening by flexural stresses.

The northernmost segment of the Karakoram fault is an active normal dextral wrench fault that bounds the Muji-Tashgurgan Pliocene-Quaternary basin (eastern Pamir). The Kongurshan (7719 m) and Mustaghata (7546 m) mountains are interpreted as twin crustal ramp anticlines formed en echelon on the eastern side of the Karakoram fault by subduction of the Tarim lithosphere under the Pamir. West-dipping S/C mylonitic gneisses that have downdip stretching lineations form the western flank of Kongur Mountain. Kinematic criteria consistently indicate a top-to-the-west sense of shear. The mylonitic foliation is cut by a steeper active normal fault, which is marked by prominent triangular facets on west-facing spurs. The ductile normal shearing deformation occurred during the interval 5-1 Ma. Therefore, like the Himalayas, the Pamir mountain range shows the coeval development of frontal thrusting and rear normal faulting. The Kongur fault thus appears to be an excellent example of synorogenic extension where normal faulting contributes to relief.

Late Precambrian glaciation in West Africa is now suggested to have extended as far south as Gibi Mountain in west-central Liberia, 200 km farther south than previously recognized glacial deposits in central Sierra Leone. The Gibi Mountain Formation includes a basal diamictite, interpreted as a probable tillite, and overlying shallow-marine laminites containing isolated, ice-rafted dropstones and dropgrains. These rocks rest on Late Archean age gneisses and are overlain by Late Archean? age quartzite klippen emplaced during the pan-African orogeny (ca. 550 Ma).

In many high-temperature (>800°C) granulite terrains, the development of characteristic horizontal structures occurred during the metamorphic culmination and was followed by isobaric cooling. The absolute magnitude of isobaric cooling (commonly >300°C) implies cooling intervals of the order of the thermal time constant of the continental lithosphere (~100 m.y.). Such prolonged isobaric cooling implies that no significant erosional denudation followed the development of the horizontal structures and thus precludes the prograde deformation being responsible for significant crustal thickening. Rather, the prograde deformation more probably records bulk crustal thinning during extensional collapse of a previously thickened crust possibly triggered by detachment of a thickened thermal boundary layer at the base of the lithosphere. -Author

In 1878, Albert Heim published a monograph on the structure of the Todi-Windgallen Range (eastern Helvetic Alps, Switzerland) containing a section entitled “The mechanical transformation of rocks during mountain building,” which is a survey and synthesis of structural geologic principles of remarkably modern tone, the prototype of many modern textbooks. Starting from basic concepts and questions–stress, strain, strength, state, pressure, brittle versus ductile behavior–Heim surveyed the results of rock deformation in nature in order to arrive at a general theory of mountain building. A complete spectrum of the minor structures resulting from fracture and flow in the Earth9s crust was reviewed, and their relation to major structures was discussed. The morphology of folded layers and the distribution of minor structures in large-scale folds were combined with a clear concept of competence to interpret the mechanism of folding in the area studied. Heim showed that the distribution of brittle and ductile features in space, combined with physical theory and experimental data, support the concept of the latent ductility of all rocks below a certain depth in the Earth9s crust and the idea of “lithostatic” pressure. These and other aspects of his theory raise the question, How did it take 100 years to accomplish our relatively modest advance in understanding?

A newly discovered vertebrate fossil assemblage, the Casa Blanca local fauna, comes from the Laredo Formation, Claiborne Group, of Webb County, Texas, and is the first reported Eocene land-mammal fauna from the coastal plain of North America. The mammalian fauna is correlated with the Serendipity and Candelaria local faunas of west Texas, the Uinta C faunas of the Rocky Mountains, the Santiago Formation local fauna of southern California, and the Swift Current Creek local fauna of Saskatchewan. The vertebrate-bearing deposit lies about 32 m above a horizon containing the marine gastropod Turritella cortezi , which ranges from east Texas to northeast Mexico in the lower half of the Cook Mountain and Laredo Formations and is a guide fossil to the Hurricane Lentil in the Cook Mountain Formation. Nannoplankton found in these middle Eocene formations belong to the upper half of Nannoplankton Zone I6 and allow correlation with European beds of late Lutetian to early Bartonian age.