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Detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice-marginal sedimentation in large ice-contact glacier-fed lakes. The input to the ice-marginal environment directly from the glacier included subglacial till and subaquatic flow tills. The subaquatic flow till (thinly bedded diamicton) was deposited in an apron (up to 1 km wide) along the ice margin. An upward gradient of pore-water pressure immediately beyond the ice margin, causing heaving and dilation of the sediments, initiated debris flows of glacially derived debris (subaquatic flow tills). Most of the stratified sediments in the ice-marginal zone entered the lake by way of a large proglacial stream. Sedimentation was dominated by quasi- or near-continuous density underflows that resulted in the deposition of a sequence of thick rhythmites. The glacier in the Lake Erie basin most likely behaved like an ice stream, with its movement controlled predominantly by a deforming bed of glacial debris, separating the glacier sole from underlying predeposited sediments. The deforming bed is preserved as a massive diamicton layer, interpreted here as subglacially deposited till.

Outcrop and continuous core descriptions, high-resolution seismic profiling, and downhole geophysical data are integrated with detailed mapping to update sedimentary and stratigraphic frameworks for Halton sediment, a complex mud-rich lithofacies succession. Halton sediment has a gradational transition from underlying Oak Ridges Moraine (ORM) sediment and can abruptly overlie Newmarket Till. Halton strata thin and fine upwards from ORM sand and gravel to graded sand, silt, and clay rhythmites, with muddy diamicton and sand and gravel interbeds. These strata fill basin lows and drape ORM sediment lobes and Newmarket Till drumlins. These distinct sedimentary units are here informally referred to as Halton formation. Formal Halton Till is a proposed subunit of Halton formation, a clay-rich diamicton mapped from Niagara Peninsula to ORM and eastward. Halton Till has traditionally been inferred to represent a late, climatically induced readvance of grounded ice from Lake Ontario basin, which deposited drumlinized till. Halton sedimentary architecture and facies are interpreted as deposition in an ice-marginal or subglacial lake bounded by Niagara Escarpment, ORM, and grounding line oscillation of a semi-buoyant ice shelf or ice lid over Lake Ontario. Large volumes of transported mud are distal equivalents of ORM high-energy gravelly sand deposits to the east. Glaciolacustrine sedimentation is indicated by mud-rich texture and laminations. Clay–silt rhythmites, diamicton interbeds, and intraclasts indicate ponding, debris flow, and periodic ice loading. Halton depositional model may apply to other muddy diamictons in Great Lakes basins. Halton formation facies are not compatible with proposed grounded ice stream events in Lake Ontario basin.

North Atlantic Heinrich events, which dispersed widespread sediment plumes and icebergs, originated principally from Hudson Strait ice streams of the Laurentide Ice Sheet. The dynamics and extent of these ice streams across the wide continental shelf seaward of Hudson Strait are not well understood. High-resolution airgun seismic reflection profiles from the outer shelf and slope show an acoustically incoherent, prograded unit at least 30 m thick. This unit has been sampled by piston cores and corresponds to a carbonate-rich diamicton unit interpreted as a glacigenic debris flow, locally overlain by carbonate-rich mud turbidites, dated as corresponding to Heinrich event 3 (H3). Younger glacigenic debris flow deposits are lacking. These data are compared with the seismic-stratigraphic record on the continental shelf, where a regional erosion surface at 10–200 m depth below the sea floor truncates Tertiary strata and is overlain by a 50 m thick diamicton (?subglacial till) sheet and is correlated with the H3 glacigenic debris flows. Above this unit, at least two distinct diamicton sheets terminate on the inner continental shelf. These data imply that grounded Laurentide ice crossed the continental shelf during H3, delivering large amounts of diamicton to the continental slope, but during the younger Heinrich events H1 and H2, no detectable record of diamicton was left on the outer shelf or slope. These findings account for observed differences between H3 and younger Heinrich events in the Labrador Sea.

A multi-proxy lithostratigraphic record from Piper Lake, Nova Scotia reveals environmental variability during the Late Glacial and Holocene. Piper Lake is a small, shallow (3 m), closed dystrophic basin located in the eastern Nova Scotia Highlands. The site was deglaciated about 14.5 cal (calibrated) ka BP and elevated loss on ignition values and relatively low carbon/nitrogen (C/N) isotope ratios indicate the establishment of a productive aquatic environment consistent with Allerød warming. The Late Glacial Lake record is punctuated by two thin, very fine-grained clay layers that are correlative to the Killarney and Younger Dryas (YD) oscillations; they were deposited when perennial ice covered the lake. The post-YD lithostratigraphy indicates the rapid establishment of an increasingly productive and stable landscape. This trend is reversed three times during the Holocene by minerogenic units. A complex 25 cm thick diamicton unique to Piper Lake was deposited ca. 10.8–10.3 cal ka BP by slumping that was associated with periglacial slope processes and (or) lake level changes; a direct correlation to early Holocene (Preboreal) cooling appears unlikely. Two thin minerogenic units deposited at ca. 8.1 and ca. 4.9 cal ka BP were likely the result of regional cooling and are broadly correlative with events noted in the GISP2 (Greenland Ice Sheet Project 2) ice-core record. The Holocene lithostratigraphic record from Piper Lake may be a consequence of unique limnological factors. Alternatively, the strong lithostratigraphic response may be the result of the absence of a strong and persistent regional climate mechanism (North Atlantic oscillation?), which if present might have obscured the impact of hemispheric or larger-scale climate forcing.

An areally extensive volcanic mass-flow deposit of Pleistocene age, known as the Chetaslina volcanic mass-flow deposit, is a prominent and visually striking deposit in the southeastern Copper River lowland of south-central Alaska. The mass-flow deposit consists of a diverse mixture of colorful, variably altered volcanic rocks, lahar deposits, glaciolacustrine diamicton, and till that record a major flank collapse on the southwest flank of Mount Wrangell. The deposit is well exposed near its presumed source, and thick, continuous, stratigraphic exposures have permitted us to study its sedimentary characteristics as a means of better understanding the origin, significance, and evolution of the deposit. Deposits of the Chetaslina volcanic mass flow in the Chetaslina River drainage are primary debris-avalanche deposits and consist of two principal facies types, a near-source block facies and a distal mixed facies. The block facies is composed entirely of block-supported, shattered and fractured blocks with individual blocks up to 40 m in diameter. The mixed facies consists of block-sized particles in a matrix of poorly sorted rock rubble, sand, and silt generated by the comminution of larger blocks. Deposits of the Chetaslina volcanic mass flow exposed along the Copper, Tonsina, and Chitina rivers are debris-flow deposits that evolved from the debris-avalanche component of the flow and from erosion and entrainment of local glacial and glaciolacustrine diamicton in the Copper River lowland. The debris-flow deposits were probably generated through mixing of the distal debris avalanche with the ancestral Copper River, or through breaching of a debris-avalanche dam across the ancestral river. The distribution of facies types and major-element chemistry of clasts in the deposit indicate that its source was an ancestral volcanic edifice, informally known as the Chetaslina vent, on the southwest side of Mount Wrangell. A major sector collapse of the Chetaslina vent initiated the Chetaslina volcanic mass flow forming a debris avalanche of about 4 km3 that subsequently transformed to a debris flow of unknown volume.

Discussion In referring to several large moraine belts n Arctic Canada, Dyke and Savelle (2000) state “a consensus is emerging that these moraines are cored by glacier ice” (p. 615). They further state that ice-cored morainal belts in Arctic Canada “would resemble southern areas of hummocky moraine were they to lose their ice cores” (p. 617). More investigation and research is required before these statements can be accepted in lieu of theories proposed by other investigators for the origin of ice within hummocky Arctic topography and for the evolution of this topography. The claimed consensus is that of Dyke et al. (1992), Sharpe (1992), and St-Onge and McMartin (1995). Dyke et al. (1992) stated that many of the moraines present on Prince of Wales Island consist of buried glacier ice. Sharpe (1992) reported exposures of relatively debris-free ice containing a few debris-rich bands underlying up to 2m of diamicton within areas of hummocky moraine. He noted the contact between the diamicton and ice as abrupt. St-Onge and McMartin (1995) reported icy sediments overlain by bouldery diamicton with a sharp and subhorizontal contact; reticulate ice was noted in the diamicton near the contact. All contacts between till and ice appear characteristic of segregation ice developing in the base of and under a finetextured soil (Mackay and Dallimore 1992). In addition, the above sequences are the reverse of the normal continental glacier sequence, where relatively clean glacier ice overlies debris-rich glacier ice. St-Onge and McMartin believed (i) the hydrogeochemistry and isotopic values of reticulate ice, ice-wedge ice, and the observed icy sediments and (ii) the slope of the co-isotope plot from their icy sediment samples support a glacial origin for the icy sediments. The latter is the strongest argument for a glacial origin of the icy sediments as the slope is similar to that for meteoric water (Lorrain and Demeur 1985). However, differentiation of segregation ice and glacial ice by co-isotope relation has since been seriously questioned (French and Harry 1990; Mackay and Dallimore 1992). The hydrogeochemistry and isotope values reported by St-Onge and McMartin (1995) for the different ice types simply confirm different origins of the ice types and do not necessarily indicate a glacial origin for the icy sediments. Dyke and Savelle’s (2000) analysis of ice-cored topography excluded the mainland west of the Amundson Gulf, where a hummocky belt of topography on the Tuktoyaktuk Peninsula and adjacent areas (Fig. 1) was studied in detail by Mackay (cf. 1963, 1971, 1973, 1983) and his colleagues (Mackay and Stager 1966, Rampton and Mackay 1971, Rampton 1974, Rampton and Bouchard 1975, Gell 1976, Rampton 1988a, 1988b, Dallimore and Wolfe 1988, Mackay and Dallimore 1992). They concluded that the ice cores found within hummocky morainal topography along the Tuktoyaktuk Peninsula and Yukon Coastal Plain (Rampton 1982, Pollard and Dallimore 1988, Harry et al. 1988) are intrasedimental ice. The conclusion is based on evidence summarized in Rampton (1988a) and Mackay and Dallimore (1992), namely — similar geochemistry and isotope values for massive ice and ice within the underlying sandy sediments in numerous profiles, indicating a common water source and downward freezing; isotope plots having linear trends through ice and underlying interbedded sand and ice and co-isotope plots showing a linear trend down through till, ice, and sand, both trends suggesting downward freezing; petrographic data from massive ice indicative of a segregation origin; the common presence of reticulate ice within the till immediately over the massive ice (reticulate ice develops in fine-grained sediments as permafrost aggrades); the asso

The Fraser River valley near Clinton contains a thick sediment fill that is presently incised down to bedrock. The sequence, approximately 500 m thick, is generally upward fining and consists of up to 100 m of glacigenic debris flow diamicton and glaciofluvial–deltaic gravel and sand at the base, overlain by about 350 m of glaciolacustrine sediments and minor diamicton, which is in turn capped by several metres of till. The sequence is interpreted to represent (i) valley aggradation in response to glaciation, followed by (ii) the impoundment of the valley by sediment and (or) ice, and the formation of a large proglacial lake(s), and finally (iii) overriding of the valley fill by glaciers. This glacial advance sequence can be readily correlated with previously studied units situated immediately to the north, most of which have been associated with the last glaciation; however, the age of these units has been based only on stratigraphic relations. We introduce limiting optical ages from a widespread glaciolacustrine unit that show that the glacial advance sequence was formed, at the earliest, during the penultimate Okanagan Centre Glaciation (oxygen isotope stage 4; ca. 74–59 ka), but almost certainly during the (last) Fraser Glaciation (oxygen isotope stage 2; ca. 24–12 ka). It could not have been deposited during oxygen isotope stage 6, or during an older glaciation.

Stratigraphic and sedimentological analyses of exposures through a glacilacustrine sedimentary sequence along the south shore of Barrier Lake, Kananaskis Country, reveal evidence of glacitectonic disturbance, relating to a readvance of the Bow Valley glacier at the end of the last glaciation. Prior to disturbance, palaeocurrent measurements in gravel and sand foreset beds record the deposition of subaqueous fans-deltas from a glacier lobe retreating eastwards along the Barrier Lake depression. The fan-delta sediments fine upwards into ripple- and cross-bedded sands and laminated muds with dropstones, documenting progressively distal sedimentation. Palaeostress directions measured from large-scale folds, shear zones and glacitectonites, and deformation tills indicate that glacier ice readvanced southwards from a glacier lobe located over the Barrier Lake depression. These stress directions are used to reconstruct the flow lines within the southern margin of a low-profile glacier lobe that terminated halfway up lower Barrier Lake, a more extensive readvance than previously envisaged in the area for this period. Comparisons of diamicton and glacitectonite fabric shapes with similar sediments elsewhere indicate that the subglacially deformed material that caps some of the sections is immature and has undergone short travel distances. Although the exact age of the readvance is unknown, it probably represents the Canmore Readvance of the Late Wisconsinan glaciation.

An investigation of diamicton units exposed in an extensive accumulation of volcanic debris in the Squamish valley, west of Mount Cayley volcano, has yielded evidence for at least three major debris avalanches, initiated by the collapse of the western flank of Mount Cayley in the mid-Holocene. Radiocarbon ages obtained from tree fragments contained in the deposits indicate that the events took place at 4800, 1100, and 500 BP. All three debris avalanches dammed the Squamish River and formed temporary lakes upstream of the debris. Failure of the cone took place after considerable dissection of the original edifice had exposed weak pyroclastic materials at the base of the steep upper slope of the volcano. No evidence of older debris avalanches from Mount Cayley has been discovered. Smaller scale debris avalanches probably have been common, and at least two have occurred in historic time (1963 and 1984). Debris avalanches from Mount Cayley and the effects of a possible damming of the Squamish River are major geomorphic hazards to public safety and economic development in the Squamish valley.

Shore bluffs at Mohawk Bay, southern Ontario, reveal, within a complex mélange of glacial sediments, brecciated diamicton surrounding sand-block intraclasts. Typically, each intraclast has an aureole (50–65 cm) of brecciated diamicton. It is thought that a causal link exists between the origin of the intraclasts and the deposition of the diamicton. A hypothesis is developed in which sand deposits are thought to have been frozen, eroded, entrained, and eventually deposited within a deforming subglacial or glacio-aquatic debris layer. These sand blocks remained frozen after being deposited, forming intraclasts encased within the diamicton. It is proposed that differential cryostatic stresses developed at the interface between the frozen blocks and the diamicton, causing tensile stresses to develop over short distances and fracturing (brecciation) of the rapidly cooling diamicton. To test this hypothesis, a simple heat-flow-simulation program (COLDSPOT) was run using parameters akin to those found at Mohawk Bay. Results from the simulation are compatible with field observations. The findings from Mohawk Bay have significant implications for glacial sedimentology and glacier bed conditions.

Soil stratigraphical and pedological techniques were used to examine the evolution of paleosols in the Highwood River Basin of southern Alberta. The paleosols were located on three types of glacial deposits: glacio-lacustrine, glacio-fluvial, and diamicton. Before the deposition of Mazama tephra at 6600 year B.P. (prior to 6600 years B.P.) episodic colluviation occurred on sloping sites, with paleosols forming during depositional hiatuses. Level surfaces were stable, allowing formation of thick, well-developed paleosols. Eolian deposition occurred on all surfaces during the last 6600 yr. The morphological and analytical characteristics of the paleosols differ depending on the influence of topography on the geomorphic processes occurring at the site. The variability in paleosols in this area limits the type of paleoenvironment information which can be inferred from paleosols. Key words: Holocene soil, paleosol, soil genesis, landscape position, soil geomorphology

This paper describes the principal glaciolacustrine deposits of a sequence of overlapping ice-marginal lakes known as glacial Lake Richardson and its transition to a postglacial sea following the retreat of a lobe of the Laurentide ice sheet from the Richardson and Rae River basin. The glaciolacustrine to marine transition is characterized by an upward-fining sequence of facies deposited in proglacial lacustrine environments, succeeded by an upward-coarsening trend corresponding to a regressive marine sequence. A composite stratigraphic section includes (a) basal diamicton, (b) stratified subaqueous sand and gravel, (c) glaciolacustrine silty clay rhythmites, (d) massive marine silty clay, and (e) littoral marine sands. The sudden passage from lacustrine to marine environments is reflected in the abrupt change in depositional mechanisms. Turbidity currents prevailed in the proglacial lake as inferred from thick sequences of varve-like couplets, whereas the salinity of marine waters, impeding the sedimentation of fines by density underflows, led to the deposition of massive structureless marine silty clays by flocculation.

It was with great interest that I read the recent article by Westgate, Chen, and Delorme reporting on the discovery of ostracode fossils in the Sunnybrook diamicton in the MetroToronto region of southern Ontario. I have followed the ongoing controversy surrounding the interpretations of the depositional origin of the sediments in the Metro-Toronto area, as I think most Canadian Quaternary geologists have. I therefore wish to comment on a number of points brought out in the article.

Geomorphic, stratigraphic, and sedimentologic evidence obtained from Quaternary sediments near Jasper, Alberta, is used to reconstruct depositional environments in the vicinity of two former confluent valley glaciers. Sedimentation occurred mainly in the valley centre in a pre-existing river channel. Lateral ice-marginal sedimentation along the inset valley walls was important during both the advance and the retreat stages. Prior to and during glacial advance, horizontally stratified gravels, sands, and silts were deposited in a braided stream. Near the valley bottom, diamictons containing trough-shaped sand lenses were deposited by subsequent proglacial debris flows and intermittent fluvial activity. At higher stratigraphic positions, outwash deposits confined to the valley wide are unconformably overlain by massive diamicton, interpreted as subglacial till, deposited as ice began to override the area. The diamicton grades towards the valley side into ice-contact debris deposited at the margins of the expanding glacier by water and sediment flows from the ice surface. Glaciers eventually overrode the entire area. During deglaciation, thick sequences of normally faulted, steeply dipping sand, gravel, and clast-rich diamicton were deposited in a kame terrace west of Jasper townsite. The orientation of bedding and faults and the nature of the sediments indicate they were derived from, and deposited in contact with, a linear belt of stagnating, debris-covered ice that extended along the valley centre east of Jasper. It is postulated that the stagnating ice originated from a well-developed medial moraine and debris septum that formed at the confluence of the large Athabasca and Miette valley glaciers. The knob-and-kettle topography, which eventually developed in the valley centre, was obscured by glaciofluvial and fluvial activity. A linear chain of kettle lakes remains as evidence of the possible existence of the moraine. Kettle chains and hummocky topography, formed in the positions of both medial and lateral moraines, may be relatively common geomorphic features in glaciated mountain valleys.

Glaciomarine diamicton(ite)s that contain articulated unbroken shell remains are usually assumed to have been deposited by the settling out of suspended mud with additions of coarse clasts derived from the melting of debris-laden floating ice. However, little is known about the magnetic and pebble fabrics of these composite sediments, and the purpose of this study is to describe and interpret the magnetic and pebble fabrics of fossiliferous glaciomarine diamictons found at three locations in the Champlain Sea, Ontario.At two of the three sites examined it is found that the long axes of the prolate and blade-shaped pebbles do not show well defined alignments, but they are not randomly distributed in either the horizontal or vertical planes. This observation and an analysis of the alignment of the magnetic particles in the matrix of the diamictons show that the diamictons have undergone syn- or post-depositional movement and fall into the category of glaciogenic subaquatic debris flows. At the third site the diamictons are stratified, and the magnetic fabric and field evidence show that post-depositional movement was caused by loading of sand layers into underlying muds.The results suggest that magnetic fabrics can be useful in interpreting pebble fabrics and that the dual approach may help to differentiate various types of glaciomarine diamicton(ite)s.

An 8 m long pod-shaped mass of deformed diamicton and sand occurs in Lake Maumee III glaciolacustrine sediments of the Port Stanley Drift, near Port Bruce, Ontario. Sedimentary structures observed in the diamicton mass and enclosing sands indicate large-scale loading accompanied their deposition. The lithology of the mass resembles admixed Port Stanley and Catfish Creek tills, which occur in moraines and other bodies of drift nearby. The diamicton mass may have been deposited en masse from seasonal or glacial floating ice or by subaquatic sediment gravity flow from floating ice or local moraines.

Two opposing interpretations have been made on the depositional origin of the Late Pleistocene Sunnybrook diamicton in the Metro-Toronto region of southern Ontario. The traditional view holds this deposit to be a till, but more recent arguments advocate a glaciolacustrine origin by suspension deposition and ice rafting.The discovery of a low-diversity ostracode fauna consisting of Candona subtriangulata, Candona caudata, and Darwinula stevensoni in the Sunnybrook diamicton suggests a lacustrine origin. Excellent preservation of thin, fragile shells and a mixture of juveniles and adults in sediments of varying texture—clayey silt to silty clay—indicate that there has been little winnowing or selective sorting and that the ostracodes are in situ. Indications are that the Sunnybrook diamicton was deposited in a large, deep, and cold lake.These new palaeontological observations call for a reassessment of the Quaternary stratigraphy of the Ontario Basin and suggest that the Laurentide Ice Sheet in the eastern Great Lakes region was less extensive during the early part of the Wisconsin Glaciation than previously assumed.

The early Wisconsinan Sunnybrook Till is a mud-rich, pebble-poor, dark gray to gray–brown massive diamicton that is exposed in the Scarborough Bluffs, Ontario. It is interpreted here to be till.Previous separate, magnetic, and pebble fabric studies made on the till suggest a westward ice movement ranging from west of south to northwest. In this study, two dominant directions are found, northwest by west and northeast by north. Of these two directions, the northwest by west direction is the most common and this combined with the direction of shear in the underlying sediments and lithology of the till suggests that the glacier moved in a westerly direction.However, the fabrics are not typical of a lodgement till and to some extent resemble fabrics found in subaquatic debris-flow deposits. It is suggested that the glacier that deposited the Sunnybrook Till was buoyed up by high pore water pressure in the accumulating sediment at the sole of the glacier. Under these conditions, the till either flowed away from the zone of release at the base of the glacier and (or) was being lightly smeared by a partially grounded glacier.

A saprolite deposit and the overlying soil profile developed in a glacial diamicton were sampled near Mount Orford, Southern Quebec. The two materials differed mainly by the magnetic mineral and extractable Al contents, by the Fedithionite/Feoxalate ratio and by the mineralogical composition. Illite and chlorite were the dominant clay minerals in the till whereas muscovite and kaolinite were the major minerals in the saprolite. A comparison was also made with another previously described saprolite deposit 4 km away from this one, in which chlorite was slightly transformed to smectite. It is suggested, from the mineral assemblages, that the two saprolites have probably formed at different times, the first one during Tertiary and the second one during an interglacial stage. Key words: Saprolite, glacial diamicton, kaolinite, muscovite, Tertiary alteration

The sampling of nonlithified diamictons for magnetic analyses (anisotropy of magnetic susceptibility and paleomagnetic remanence) has been restricted to samples that are either massive, clay-rich sediments, or fine-grained ones with very low pebble contents. A new method was developed that produced standard-sized 2 × 2 × 2 cm cubes of sediment from a laminated, clay-poor diamicton from southern Denmark. The sampling procedure did not affect the sample or its magnetic characteristics in any observable manner.

Hicock et al. describe complex submarine outwash cones from Quarternary glacimarine exposures. I do not question their interpretation of the diamicton sediments in the cones as being submarine flows or slumps from glacial debris; indeed, their descriptions are invaluable for tidewater glacier facies modelling. However, I have some comments on the suggested origin of the flows. Several different configurations of tidewater ice fronts may exist, but few allow the formation and preservation of sediment gravity flow deposits that originate subaerially and flow into the sea. Under polar conditions where glaciers cannot maintain themselves as floating ice tongues or ice shelves, they end in very shallow water and a beach is constructed at the base of their cliffs (e.g., Sugden and John 1976, Fig. 11.94. Most debris is slowly melted out, but rarely flowage may occur. However, such material is highly likely to be reworked by waves and, further, the ice margin in Puget Sound that Hicock et al. describe was probably not under polar-type conditions. In my experience of modem temperate tidewater glaciers in Glacier Bay, Alaska, only restricted conditions allow thick accumulation of supraglacial melt-out tills from englacial debris layers. Ablation of tidewater glaciers occurs more by berg calving rather than upper-surface melting, and ice fronts (at least above tide level) are nearly vertical cliffs. Ice is very crevassed back from the face, and the free face with consequent extensive flow commonly creates large transverse crevasses. Englacial debris layers are exposed across an ice face rather than transversely across the upper surface. However, the sides of each layer may intersect the upper surface of a glacier snout to form supraglacial melt-out debris parallel to the valley walls. Other supraglacial debris is primarily from rockfalls off valley walls and is rubble rather than diamicton. Rarely, some debris flows down the face from the upper edge, but the steepness of slope ensures sorting and separation of particles as the flow proceeds. The larger mass of pebbles and coarse-grained sand particles causes them to fall faster

Hicock proposed an origin for the carbonate till in the Hemlo area of Ontario that is incompatible with the statistical study of attrition of Paleozoic clasts in a carbonate till between Hamilton and London, Ontario; with the occurrences of limestone mapped along Highway 17 north of Lake Superior by M. Tremblay (consulting geologist, personal communication, 1987); and with the occurrence of Paleozoic limestone at the foot of Boot Bay, Kabinakagami Lake, Lizar Township, mapped by Wahl (1954). Vagners (1969) described the attrition in size and shape of Paleozoic carbonate clasts in the till between Hamilton and London. The clasts in this till are composed predominantly of Paleozoic sediments, and the clasts achieve a roundness and become part of the matrix in the matter of a few kilometres. Hicock describes his calcareous till as a dark grey, compact, fissile, stoney, calcareous diamicton with a matrix of up to 35-40% carbonate. The clasts are described as being subrounded to subangular and to consist of Paleozoic and Proterozoic lithologies in equal amounts. It is difficult to understand how Paleozoic and "Proterozoic" debris could have been encapsulated as a large blob of debris within the ice north of Hearst and transported as a unit more than 150 km without some attrition in size or a change in form. It is especially difficult to understand when one considers the differences in hardness of the two lithologies. Further, it is difficult to understand the origin of the Proterozoic clasts in the till, as the Ontario Geological Survey has mapped only Archean rocks up glacier from Hernlo. However, Proterozoic rocks do occur southeast of Winisk. Surely these rocks are not the source of the Proterozoic clasts. While mapping the magnetite deposit east of Boot Bay in Lizar Township for Neoscope Exploration in 1954, I found Paleozoic limestone underlying the southwest portion of the bay. This bay is approximately 140 km down glacier from the exposed Paleozoic rocks on the edge of the James Bay basin (Wahl 1954). About 1965, M. Tremblay (personal communication, 1987) mapped the heavy minerals in the till between Hearst and Long Lac north of Lake Superior. He reports mapping Paleozoic limestone along Highway 17 north of Lake Superior. On a practical note, drift prospecting is hindered not only by the presence of carbonate till in the Hernlo area, but also by the Paleozoic limestone from which it was derived.