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The coal-bearing late Palaeozoic Gondwana basins in Eastern India are surrounded on all sides by Precambrian basement rocks. These basins are aligned in three regional trends — a West-East Damuda trend, a minor Northwest-Southeast Mahanadi trend and a narrow Northwest-Southeast Godavani trend. In these regional trends differential subsidence in individual areas gave rise to localized steeper palaeoslopes. The Giridih Gondwana basin is one such basin that is aligned with the major West-East trend. As in most Gondwana basins, the oldest basal unit that immediately overlies the Precambrian basement is a boulder bed which was hitherto thought to represent a till of obvious glacial derivation. Close examination, however, reveals that the till is not typical but shows rudimentary stratification, and is comparatively better sorted than the unsorted tills. Because of its sorted nature, it is suggested to name the boulder bed a matrix-supported diamictite deposited as a debris flow during the retreating phase of the glacier. The deeper northern part of the Giridih basin is occupied by a weakly laminated to massive diamictite interpreted as undermelt diamictite, a product of an advancing phase of the glacier. The topmost beds consist of laminated diamictites and rhythmites that were deposited at the time of glacial retreat. The southern boundary of the Giridih basin has gentle slopes and here the sediments consist of a massive, graded conglomerate which is succeeded by lenticular diamictite and aeolian sandstone. The conglomerate and sandstone are considered as channel deposits deposited by different types of gravity flow. The youngest aeolian sandstones are non-glacial obviously deposited during the final inter-glacial period. The glacier that deposited the sediments is of the piedmont type which advanced into the basin from the south, southwest and west. At least three well defined phases of glacial advance and retreat could be recognised in the basin. Diamictite III represents the last glacial advance into the basin.

The study of lithological associations, sedimentary structures and their interrelation suggests that the Talchir rocks of the Sahajuri Gondwana basin were deposited in a proglacial lake. The lowermost lithological association of diamictites and chaotic boulder beds deposited mainly as sediment gravity flows, represent a transitional phase between terminoglacial and proglacial sub-environments. The coarsening-upward sequence, coarse steeply dipping sandstone and fining-upward sequence together represent bottomset, foreset and topset, respectively, of a Gilbert-type delta. The delta progradation to the southwest was mainly controlled by decaying of buried ice in the lake floor and consequent enlargement of the lake. The diamictites were emplaced mainly as debris flow and the chaotic boulder bed by downslope slumping.

Mahadeva Formation (Triassic) rocks in India occur as scarp-forming, red-coloured steeply dipping (average 20–28°, maximum 33°) cross-stratified sandstone. From the lithofacies study and comparison with known ancient aeolian sandstones and modern desert sands, it is suggested that the Mahadeva sandstone is the depositional product of an aeolian environment. Two major facies—dune and wadi sediments—form the major portion of the stratigraphic column. Study of cross-stratification slope directions and further correction of the directions with respect to the Triassic north pole, suggest the presence of a southeasterly trade wind in the Auranga Basin during the Triassic. This trade wind was mainly responsible for dune movement and the Deposition of Mahadeva sediments; wadi channels were initiated during temporary rainy seasons from the highlands to the north and formed a number of water-deposited beds within the wind-laid beds. A three-dimensional model showing palaeolocations of Mahadeva rocks within a desert model is presented.

Study of bedforms, facies and associated sedimentary structures in the Talchir rocks of Taratanr Lower Gondwana basin suggests that the basal Talchir Boulder bed was deposited by both ice (moraines and deltaic moraines) and braided streams of glacier derivation (outwash deposit). The overlying sandstone was deposited by ephemeral streams. Six depositional facies related to the bedforms, ripple, dune, bar, plane bed, transverse rib and current crescent, were identified. Data compared with those from modern environments, show excellent correlation with the features of modern glacial outwash plains and modern braided, high-gradient streams. A comparison of the stratigraphy and sedimentology of Talchir rocks from eight Lower Gondwana basins in eastern India suggests that the tentative basin model for Talchir deposition in the Taratanr basin may serve as a basic model for Talchir sedimentation in all the Lower Gondwana basins in eastern India.

During the Early Tertiary epoch a basin of deposition covered almost all the present Himalayan foot hill zone. Large quantities of detrital sediments were transported from the northern source area to the depositional basin. The rivers carrying the sediment load formed large delta complexes. In the area studied at least two such delta complexes, one around Kalka and the other around Nahan, were formed; of these the one around Kalka contains the greatest volume of sediments. The recognition of the deltas is based on: (a) greater abundance of stream deposits than deposits of other environments; (b) lithologic criteria, particularly sedimentary structures, repetitive lithologic associations; (c) the general coarsening-upward nature of the sediments; (d) strong unimodal current direction; (e) the typical lenticular lithogenetic model, common in recent deltas. The rocks of the Nahan Group are divisible into three formations at Kalka and two formations at Nahan where central formation did not develop. Himalayan tectonism has largely controlled both delta formation and stratigraphy. The differential rates of sedimentation greatly influenced the rates of subsidence within the Nahan basin. The sediments of the Nahan Group are roughly bounded between two major phases of Himalayan uplift, namely Eocene and middle Miocene tectonic movements. The effects of intermittent tectonic pulses are well depicted in rocks of the Nahan Group. The intensity of the tectonism that controlled both the source-area rise and basin subsidence during deposition of the Nahan Group of sediments was nonuniform, both in vertical and lateral directions. Because of a generally higher rate of deposition compared to the rate of subsidence, the rocks of the Nahan group represent a normal regressive basin-filling sedimentation, forming thick detrital deposits due to progradation of younger deltas beyond the distal end of older deltas.

The sedimentology of the Simla Series is practically unstudied. In connection with structural and stratigraphic work, Ghosh et al. (1966) gave a brief sedimentological description of the rocks and suggested that the Simla Series represent a geosynclinal sediment and that the pebbly shale horizons represented an intraformational conglomerate formed by either a turbidity current or a mud flow. Pandey and Narayan (1966) suggested that the Simla Series rocks represent flysch-type sediments. In the present study the authors describe the primary sedimentary structures, vertico-lateral variation of the sediments, etc., in greater detail. Plane laminae and the predominance of finer sediments (shale, siltstone and fine-grained sandstone) suggest a deep-water origin of the sediments. The lithological character and the sedimentary structures strongly suggest that the Simla Slate Series are turbidite deposits belonging to flysch facies.

The paper presents a new criterion for designing a power-system stabiliser, which is that it should cancel the negative damping torque inherent in a synchronous generator and automatic voltage regulator. The method arises from analysis based on the properties of tensor invariance, but it is easily implemented, and leads to the design of an adaptive controller. Extensive computations and simulation have been performed, and laboratory tests have been conducted on a computer-controlled micromachine system. Results are presented illustrating the effectiveness of the adaptive stabiliser.

Current interest in the use of combined direct- and quadrature-axis excitation-control systems for synchronous machines makes it relevant to consider the basic physics of such a configuration. By studying the synchronising and damping torques, it is possible to assess the effectiveness of this type of control.

The paper describes experimental results obtained from transient tests on a laboratory universal machine, connected to operate as a 3-phase alternator. During these tests, which were carried out in order to measure the parameters, severe harmonic distortion was found in the armature-current waveform under conditions of sudden symmetrical short circuit. This appeared to be mainly second and third harmonic together with a very low-frequency subharmonic. The paper gives an analysis of the machine with computed values of transient current and shows that, with the compromise design used to achieve a measure of generalisation, such harmonics are to be expected. It also shows mathematically that the usual transient d.c. component in the armature current may become a transient, very-low-frequency oscillation, depending on the machine parameters. These effects observed on a `universal machine? were also found during tests carried out on a second generalised machine of different design. It was found that damping and field time constant have considerable effect on the transient harmonic distortion in the short-circuit armature current.

The paper analyses the influence of various types of field regulators on the dynamic performance of synchronous generators. Both conventional and dual-excitation generators are considered, with basic controls provided by voltage and angle regulators, which may have proportionate and derivative feedback. In the case of dual-excitation machines, both bus-rotor-angle and terminal-rotor-angle signals are employed in the quadrature-axis regulator. Stability is initially defined by computed regulation curves, and additional information is then obtained by calculating the variations of the synchronising- and damping-torque coefficients (Ts and TD) with regulator gain. These graphs are superimposed on the regulation curves, to show how Ts and TD determine the dynamic stability of the machine, and to illustrate the underlying reasons for stability.

Current interest in doubly excited synchronous machines makes it relevant to consider the basic physics of a synchronous machine which has more than one field winding. In this paper, the synchronising and damping torques, which may arise in the individual windings of a large turbogenerator, are examined analytically for a number of different rotor-winding configurations.

The paper investigates synchronous-machine damping and synchronising torques analytically and experimentally, in two distinct reference frames. The first is that of Park and the second is a freely rotating frame used by Kron, Ku and others. it is found that the uniformly rotating free frame presents a clear picture of the nature of the torque components and the sources of these during hunting conditions. The analysis has been confirmed by tests on a laboratory machine.