On the basis of stratigraphic, tectonic, and metamorphic studies in certain critical Pre-Cambrian areas of Nagpur-Bhandara-Drug region and twenty-six K-Ar age data of representative samples, the authors have suggested a new generalized succession and correlation of the dated orogenic cycles and phases, and have drawn the following conclusions:-

(a) Amgaon cycle closed during the period 1444–1730 m.y.

(b) Sakoli cycle (I phase) closed at 1330 m.y., and during Sausar orogeny (864–996 m.y.) the north-western part of Sakoli syn-clinorium was deformed and metamorphosed (862–950 m.y.).

(c) Sausars and Sakolis, both post-Amgaon in age, were deposited in separate basins and had different tectonic histories.

(d) Nandgaon folding phase (< c. 1200 m.y.) affecting Bijli rhyolites is younger than Sakoli (I phase), and Chattisgarh Cuddapahs are younger than Khairagarh phase (< c. 600 m.y.).

(e) In Bastar area Bailadila cycle closed at c. 2100 m.y.

Understanding the structural evolution of the South Dezful Embayment (SDE) in the Zagros Fold-and-Thrust Belt (ZFTB) is significant for hydrocarbon exploration and production. The structural evolution of this area has been controlled by the reactivation of basement structures related to the oblique convergence along the ZFTB. In this work, we study the effect of the pre-contractional interaction between the basement step and overlaid salt layer superimposed by the Zagros shortening on the structural style and evolution of the sedimentary basin in the SDE. We use multidisciplinary approaches involving surface and subsurface data and analogue models. Disharmonic folds with small wavelength formed over the Kharg-Mish Palaeo-high (KMPH) where the sedimentary cover is thinner. On the other hand, faulted detachment folds with large wavelengths developed in the adjacent depocenters. Furthermore, the KMPH affected the geometry and kinematics of the frontal part of the Zagros Belt, which is characterized by the Mountain Front Flexure (MFF) topographic step. Long-lasting active deformation of the sedimentary cover over the frontal ramp of the KMPH developed the South Izeh Promontory (SIP). Localized contraction in the SIP was accommodated temporally by trishear fault-propagation folding and resulted in > 5 km elevation difference between this promontory and two adjacent local basins. Supporting scaled analogue models show that structural evolution, folding and along-strike variations in fold style of the SDE have been controlled by thickness variations of the sedimentary cover and the geometry of the inherited pre-salt structure. Based on the results of this study, the effect of inherited structural highs on the structure and kinematics of the SDE provide important insights for hydrocarbon entrapment, migration and exploration.

Extensive sections in the Thorington gravel quarry complex in eastern Suffolk include the most complete record to date of sedimentary environments of the Westleton Beds Member of the Norwich Crag Formation. New palaeoecological and palaeomagnetic evidence is presented, which confirms that the Member was deposited at or near a gravelly shoreline of the Crag Sea as sea level fluctuated during a climatic ameloriation within or at the end of the Baventian/ pre-Pastonian ‘a’ Stage (Tiglian C4c Substage).

Tie-line data are presented for twelve analysed igneous pyroxene pairs, from which it is demonstrated that a precise point of intersection, at or close to Wo75 En25 in the ternary diagram, does not exist. Eight tie-lines for pyroxene pairs from ultrabasic nodules in basalts are also considered. The tie-lines for metamorphic pyroxenes are compared with the igneous, and are shown to intersect over a similarly wide range, the average (Ca82 Mg18) being the same for both assemblages. It is shown that no conclusions can be drawn as to the genesis of the pyroxene assemblage, from the assumption of a characteristic tie-line intersection point. Optical determinations are considered, and shown to be of little practical value in this particular problem.

Northern Iceland between Skagafjord on the west and Skjalfandi Bay on the east is a deeply dissected upland built up of plateau basalts with subordinate intercalations of clastic volcanic sediments. The main valley, the Eyjafjord, is traceable northwards as a groove in the sea floor down to–500 metres. To the east of the upland the country is less elevated; marine Pliocene deposits are present in the Tjörnes peninsula, and recent lava flows are prominent. The contrasted regions adjoin along the BarQardal fault running N.–S. and marking the western boundary of the great graben which has been the site of Recent and Quaternary volcanic activity. Thoroddsen considered the upland rocks to be Tertiary (Miocene) in age, and that the Pliocene sediments had been laid down in a bay formed after the faulting and erosion of the older series.

The Seve Nappe Complex in the Scandinavian Caledonides contains the fragmented late Precambrian continent–ocean transition between Baltica and the Iapetus Ocean. This passive margin was fragmented and thrust eastwards over the Baltic Shield during Caledonian orogenesis. The individual thrust sheets in the Seve Nappe Complex went through different P–T–t evolutions, resulting in dramatic metamorphic contrasts: eclogite-bearing nappes are juxtaposed with nappes showing no evidence of Caledonian deformation or metamorphism in their interiors. Strain localization to the marginal parts of the thrust sheets left records of both pre-orogenic (rift) and early orogenic (subduction and subsequent uplift) processes in the thrust sheets of the Seve Nappe Complex. Even though it has been transported several hundred kilometres, only the margins of the eastern part of the Sarektjåkkå Nappe are affected by penetrative Caledonian deformation. This part of the Sarektjåkkå Nappe is dominated by pristine tholeiitic dykes and cross-bedded sandstones. The dykes are 608±1 Ma old and make up 70–80% of the nappe. Widely spaced thin shear zones of the Ruopsok fault system represent the only Caledonian penetrative deformation in the interior of the nappe. Previously published Ar–Ar dates indicate cooling below the closure temperature of hornblende at c. 470 Ma, but numerous ages have been recorded. Ar dating of biotite and muscovite from a cross-laminated metapsammite in the Sarektjåkkå Nappe gave well-defined ages of 428.5±3.6 and 432.4±3.8 Ma, respectively. Muscovite from a shear zone in the Ruopsok Fault System gave 428.2±4.0 Ma, whereas hornblende from the same locality did not yield interpretable data. The results indicate that these rocks were completely degassed at some unknown time, presumably at the emplacement of the dyke swarm. No subsequent excess argon contamination can be detected. A likely candidate for the degassing event is the emplacement of the dykes at 608 Ma. The interior of the nappe, and thus the entire nappe complex, cooled below ∼ 350 °C at around 430 Ma. Cooling from more than 500 °C at c. 470 Ma to 350 °C at c. 430 Ma suggests an average cooling rate of [les ] 4 °C/Ma. A prolonged period of slow cooling (≈exhumation?) following the initial, rapid uplift of the eclogite-bearing nappes and Early Ordovician construction of the Seve Nappe Complex is suggested.

Petrographic and geochronological studies of the rocks of Bulland Hill, an inlier of basement in the Punjab alluvium, are reported. Acid and basic pyroclastic and high-level intrusive types give an Rb–Sr isochron age of 870±40 million years. The previous correlation with the Malani Rhyolite Series of north-western India must be abandoned.

A porphyry boulder from the Permo-Carboniferous boulder bed, probably a tillite, in the Salt Range has the same age as the Bulland Hill rocks.

Early in January, 1916, Dr. O. P. Hay, of Washington, D.C., referred to me for description the fossil bone of a large bird that had been discovered in the eastern part of South Carolina some time previously. This specimen I at once recognized as the lower extremity of the right femur of some bird belonging to a species much larger than any existing form in the United States. I find this specimen to be thoroughly fossilized and of a dull-black colour, the edges of both condyles being considerably chipped off. On the antero-internal aspect the shaft appears to be cut away as if by some shaving implement. This, and where the shaft is broken nearly squarely across above, exposes a filling of a dense, very hard, pale-grey matrix, with a grain as fine as clay. Judging from this there should be no doubt but that this femur was a thoroughly pneumatic one in the living bird, and that the thickness of the osseous wall of the shaft was by no means great, as may be appreciated by examining the figures on the accompanying Plate XV.

Tinto hill by reason of its height, its massive but shapely form, and its splendid isolation, dominates the whole of middle Clydesdale. It forms an east-west ridge of tadpole-like outline—massive and lofty towards the eastern end and tailing away towards the western extremity, the only point at which it makes contact with the neighbouring uplands. On the east it rises directly from Clydesdale, where its lower slopes pass into a drift-mantled bench, which is from 1 to 2 miles in width. The lower and flatter portions of this bench are covered by a sheet of sand and gravel 30 or more feet above the Clyde flood-plain. The gravel spread extends into the broad open valleys which isolate Tinto to north and south, and is there undergoing dissection by the Glade Burn and Garf Water. The dissection is, however, hardly more than begun, and the undulating and sometimes moundy character of the surface of the gravel sheet reflects the uneven nature of the original deposition. Rising sharply from this surface are certain striking mounds and ridges which have received some mention in geological literature under the name of the Thankerton Kames. They were first noted by Sir Archibald Geikie (2, p. 44),1 and later described, with a map indicating their extent and distribution, by Professor Gregory (3, p. 474). They have been further discussed by Professor Charlesworth (1, pp. 31–37), who is unable to accept Professor Gregory’s interpretation of the facts. More recently they have been mapped by the officers of the Geological Survey (4), together with the better-known Kames of Carstairs, and in this connection a note by Dr. M. Macgregor on the latter (6) is of some interest.

Recently acquired deep seismic reflection profiles recorded to 12 s two-way travel time in southern Britain suggest that the crust beneath this area is commonly divisible, vertically, into three zones.These zones, based upon seismic character, can be related to structural or tectonic units. They comprise an upper zone of cover rocks of various ages, a middle zone of folded and thrust rocks, and a lower zone tentatively identified as metamorphic or crystalline basement. A sketch crustal profile from Dorset to Yorkshire summarizes the data and illustrates the distribution of the zones.

Geological survey, electron microprobe analyses of clinopyroxenes and isotopic age determinations have revealed that the intrusive dolerites and basic–intermediate lavas of the Shelve Ordovician Inlier are part of a co-magmatic suite which show transitional affinities between tholeiites and alkali basalts. The ages of most of the intrusives are shown to be mid-Ordovician.

Quartz-trachytic differentiates characterise volcanic islands on or near mid-ocean ridges, while phonolitic trends are found on islands rising from ocean basins. A large part of the Kenya Rift Valley is dominated by Plio-Pleistocene quartz-trachytes, which are underlain and flanked by variably nepheline-rich Miocene and Plio-Pleistocene lavas.

Phonolitic and nephelinitic lavas dominate the assemblages of Miocene age, trachytes and olivine basalts those of Plio-Pleistocence age. This change in petrographic character with time is attributed to two stages of sub-crustal pressure relief corresponding to Lower Miocene and late Pliocene elevations of the Kenya dome. The result was a change in partial melting products from less to more silicic, especially along the axial rift valley.

The doming movements and related vulcanism are believed to have originated because of lateral compression, induced by sea-floor spreading movements in the Atlantic and Indian oceans.

Increasing attention has been paid in recent years to the reconstruction and interpretation of stream profiles. It might therefore be well to examine a little more closely the way in which the curve of water erosion and the polycyclic valleys are produced. In this paper these problems are considered in the light of some preliminary experimental work recently described in this Magazine (1).

Five nomenclatural problems in the inarticulate brachiopods are discussed and solutions suggested for them. Two new genera, Eodinobolus, type species Obolellina magnifica Billings, 1872 and Orthisocrania, type species Pseudocrania divaricata M'Coy, 1851 are erected. Clistotrema nom. nov. for Orbicella d'Orbigny, 1847 non Orbicella Dana, 1846 is proposed.

The NE–NNE-trending Yuan-Ma Basin in central South China, an overprinted basin, is important for understanding the transition in Mesozoic intracontinental deformation in South China from compressional to extensional settings. A detailed sedimentary and structural cross-section across the basin reveals the Upper Triassic – Lower Jurassic black coal-bearing shale, greyish-green sandstone and brick-red claystone, and the Middle Jurassic brick-red sandstone, pebbly sandstone and conglomerate in the eastern segment of the basin. The Lower Cretaceous brick-red coarse sandstone, pebbly sandstone and siltstone occurred in the western and central segments, as well as fault breccia and Lower Cretaceous sandstone at the western margin of the basin. Detrital zircon U–Pb dating by laser ablation inductively coupled plasma mass spectrometry shows that the magmatic and metamorphic zircons yield significant age clusters at 900–700, 500–350 and 300–150 Ma, as well a minor age cluster at 120–100 Ma. Synthesizing the stratigraphic sequences, structures, isotopic dating results and palaeocurrent data, we infer that the Yuan-Ma Basin experienced three evolutionary stages and tectonic settings: (1) during Late Triassic – Early Jurassic time, the Yuan-Ma Basin was related to the diachronous progressive intracontinental deformation as a result of the early Mesozoic Xuefeng intracontinental orogeny in South China; (2) during Middle–Late Jurassic time, the Yuan-Ma Basin was related to intracontinental compression in South China; and (3) during late Early Cretaceous time, the Yuan-Ma Basin was constrained by the intracontinental extension that occurred in eastern China. These three stages, a result of various tectonic regimes, caused the intracontinental deformation that was controlled by the evolution of the continents and their margins.

The Posada–Asinara Line is a crustal-scale transpressive shear zone affecting the Variscan basement in northern Sardinia during Late Carboniferous time. We investigated a structural transect of the Posada–Asinara Line (Baronie) with the aid of geological mapping and structural analysis. N-verging F2 isoclinal folds with associated mylonitic foliation (S2) are the main deformation features developed during the Posada–Asinara Line activity (D2). The mineral assemblages and microstructures suggest that the Posada–Asinara Line was affected by a retrograde metamorphic path. This is also confirmed by quartz microstructures, where subgrain rotation recrystallization superimposes on grain boundary migration recrystallization. Crystallographic preferred orientation data, obtained using electron backscatter diffraction, allowed analysis of quartz slip systems and estimation of the deformation temperature, vorticity of flow and rheological parameters (flow stress and strain rate) during the Posada–Asinara Line activity. Quartz deformation temperatures of 400 ± 50 °C have been estimated along a transect perpendicular to the Posada–Asinara Line, in agreement with the syn-kinematic post-metamorphic peak mineral assemblages and the late microstructures of quartz. The D2 phase can be subdivided in two events: an early D2early phase, related to the metamorphic peak and low kinematic vorticity (pure shear dominated), and a late D2late phase characterized by a lower metamorphic grade and an increased kinematic vorticity (simple shear dominated). Palaeopiezometry and strain rate estimates associated with the D2late deformation event showed an intensity gradient increasing towards the core of the shear zone. The D2early deformation developed under peak temperature conditions, while the D2late event was active at shallower structural levels.

This petrographic and chemical study of the Hercynian granitoids of the Central Palaeozoic Massif of Morocco covers the Zaër, Ment, Oulmès, and Moulay Bouazza plutons. These plutons are formed of biotite or two-mica, quartz-rich granodiorites and monzogranites containing reddish-brown, inclusion-rich biotites as the only essential mafic mineral; zoned plagioclase; and perthitic K-feldspar. The modal contents of micas and K-feldspar are highly variable. The granitoids are generally medium to coarse grained, massive; however foliated varieties are also commonly found, particularly at the contact of the' plutons with sedimentary rocks.

The strongly peraluminous character of the granitoids is shown by high normative corundum and high molar Al2O3/(CaO + Na2O + K2O) ratio, and is reflected by the occasional presence of aluminosilicates.

The mineralogical and chemical characteristics of the granitoids are similar to those of the S-type granites, and were inherited from the crustal source of the granitic magmas which are thought to have been generated by partial equilibrium fusion of the sandy argillaceous sediments of the Massif. The heat source for the fusion might have been provided by intrusion of mantle-derived material.

The junction in Newlands Beck between the steeply dipping Skiddaw Slates striking N–S, and Borrowdale Volcanic rocks dipping gently to the SE is interpreted as an angular unconformity, and indicates the existence of pre-Borrowdale Volcanic folding. There is no cleavage associated with this folding, however, the ENE–WSW Caledonoid cleavage being the only one present, and this is common to both Skiddaw Slates and Borrowdale Volcanics.

On the basis of previous work in Northern England and in Southern Scotland the Pusgillian Stage is in turn related to the stratigraphical ranges of selected trilobite species and to the standard graptolite zonal scheme. Thus characterized it can be recognized in rocks of ‘shelly’ facies at localities in the northwest, southeast and south-central Berwyn Hills of North Wales and possibly in the Llandeilo area of South Wales, but does not seem likely to be developed in any rocks of graptolitic facies in Wales.