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___.tures and crustal structure has been the completion by E. Suess of the third volume of Das Antlitz der Erde in 1909: the annotated and " extra illustrated " French edition was published under the care of E. de Margeriein 1918. In this volume the Armorican mountain systems of Europe are regarded as offshoots of those of Asia, under the general name of Altaids. The spread of the ranges in huge south- ward ripplings towards India, and their finger-like ramifications in the European region, are shown, as well as their posthumous in- fluence on the directions of the Cainozpic chains, or " Alpids."

To E. Suess we also owe the observation of "caldron-subsidences" in many portions of the globe, from crater-like depressions, such as those traceable in lunar topography, to broad plains, the gather- ing-ground of detritus from upstanding mountain-rings. It is true that the recognition of overfolded sheet-structure in the Carpathian ring has disposed of the conception that the differential elevation of the ring and the Hungarian basin is mainly due to faulting; but there remain many lowlands in which foundering has caused the depression, and no doubt the most striking instances are concealed beneath the oceans. The Tyrrhenian and Aegean sinkings occurred almost in human times, and speculation may still be allowed to revive the ancient tradition of Atlantis. A belief in the comparative rapidity of such movements is fostered by the evidence of Fossiliferous strata on the flanks of the marine depressions and on residual isles. The down-sinking occurred during a part of one geological epoch; and the same is remarkably true for the upheaval and lateral flow of folded mountain-chains.

The well-known Rieskessel, the plain round Nordlingen in south- ern Bavaria, presents all the character of a caldron-subsidence, with a core of shattered granite, and abundant upwellings of lavas on the marginal ring (see section in Suess, La Face de la Terre, vol. 3, p. 1,507). C. T. Clough, E. B. Bailey, and H. O. Maufe, in describing the "caldron-subsidences of Glencoe" (Quart. Journ. Geol. Soc., vol. 65, 1909), show how foundering took place within a ring-fault, up which a " fault-intrusion " occurred, probably as a fore- runner of the granite that afterwards came into the district. This intrusive rock gathered into itself the fragmental matter accumu- lated along the fault-plane. The mechanics of such subsidences, and the substitution of igneous matter for the foundered core, are here clearly discussed. A striking upwelling of syenite along a ring 16 m. in diameter has been mapped by W. A. Humphrey (1914) in the Pilansberg in Transvaal.

Coral Reefs. The question of the evidence afforded by coral reefs as to regions of subsidence has been advanced by the large number of instances where barrier reefs and atolls have been shown to stand on the marginal areas of submarine platforms. The depth of the lagoons enclosed by coral rings appears to agree closely with the depth of the platform outside them. The platforms may in places be composed, as W. M. Davis suggests in the case of Queensland, of wave-planed coral rock of unknown thickness, and E. C. Andrews (1916) and W. C. Foye (1917) regard the reefs of Fiji as thickened during local subsidence. But Foye finds no proof of general subsidence during coral- growth in the Pacific; block-faulting has more probably occurred. T. W. Vaughan (Bull. 103, U.S. National Museum, 1919) discusses the whole question of the growth of reefs on platforms; the reefs have in some cases been thickened as Darwin suggested; but tectonic interest has now been shifted to the platforms. If these are of Pliocene age, they should represent an epoch of elevation and wave-erosion, and a subsequent enlargement of the oceans by subsidence. If, as R. A. Daly urges, they are Pleis- tocene, his " glacial control " theory may account for their origin at a time when the sea was lowered by withdrawal of water to form ice at the poles. But it is doubtful if the whole of the existing reefs are of post-Glacial age, and attention is thus redrawn to evidence of crust-movement in the platforms.

The economic importance of structural geology has been specially emphasized by numerous surveys of oil-bearing districts, and the entry of oil into anticlines and domes has been interestingly corre- lated in the United States with the earth pressures that caused the folding. (G.A.J.C.)

IV. STRATIGRAPHICAL GEOLOGY

The study of comparative stratigraphy has been greatly facilitated by the publication of the Handbuch der regionalen Geologic, under the editorship of G. Steinmann and O. Wilckens, the first part of which, on Denmark, appeared in 1910. Written by specialists in various countries, the descriptions and bibliog- raphies are brought fully up to date. The section on the British Isles, by 14 British geologists, was issued, as a triumph of scientific cooperation, at Heidelberg during the World War in 1917. E. Haug's Traits de Geologic (1908-11), with its wealth

of coordinated detail, has furnished an important work of general reference. Attention has been given, especially in the United States, to " diastrophic " episodes, epochs of apparently world-wide earth-disturbance, and the old theories of " revolu- tions of the globe " have been recalled by the tendency to connect diastrophism with marked changes of fauna. Many geologists have felt that the boundaries set to geological periods may be quite justly drawn at epochs of crust-movement, which promoted rapid modifications in life-forms to suit altered conditions of existence. The continuity, however, of marine Carboniferous and Permian systems in some countries, and the break caused by the Armorican folding in Europe, serve as an example of the difficulty of calling in diastrophism as a general aid in classifica- tion. C. D. Walcott (1910) explains the abrupt appearance of the Cambrian fauna by suggesting that the marine basins of pre-Algonkian time, in which earlier faunas may be recorded, have never been elevated to form part of the land-surface. The few traces of Algonkian fossils represent lakes, or merely brief communications with oceanic waters. Walcott proposes the term Lipalian for the epoch when the unknown primordial fauna was adjusting itself to shore-conditions. The Lower Cambrian fauna had thus attained a high degree of differentia- tion when the Olenellus-beds were deposited by encroachments of the sea across the continents. In nomenclature, the adoption of the name Silurian by the British Geological Survey in the restricted sense has been accompanied by a general change in the same direction, while Lapworth's Ordovician has also be- come international. E. O. Ulrich (1911) has proposed in the United States to cut off an Ozarkian system from the top of the Cambrian and a Canadian system from the base of the Ordovi- cian, restricting the term Ordovician to beds above the Beek- mantown stage of the Champlain valley and Maryland. C. Schuchert, in his last pronouncement (1915), adopts these terms as lower subdivisions of his Ordovician system.

The frequent revision of the names of local subdivisions may be illustrated by A. W. Grabau's classification in 1909:

Upper Monroan

Siluric Middle Salirian

Lower Niagaran

Upper Trentonian

Ordovicic Middle Chazyan

Lower Beekmantownian

Walcott (1912) proposed St. Croixan for the Upper Cambrian and Wacauban for the Lower, thereby replacing Saratogan and Georgian. The correlation of the Cambrian and Ordovician strata throughout the United States is shown in a detailed table in a volume issued by the Maryland Geological Survey in 1919.

Pleistocene deposits, especially in relation to evidences of the antiquity of man, have attracted considerable research, and the publication of W. B. Wright's Quaternary Ice Age (1914) has provided a philosophic summary of recent glacial observations. The most marked advance has been the general acceptance of views in which James Geikie was one of the foremost pioneers. Widely spread deposits of boulder-clay and plains of outwash gravel are no longer attributed to the agency of floating ice, but are recognized as the unmeltable residues of glaciers of the Greenland or " continental " type, the lower layers of which may consist of 50% of material gathered from the ground in their advance. A glacial epoch is now regarded as due to a cooling of the atmosphere round all the earth, and evidence of the spread of ice in Permian times, even in tropical lands, continues to accumulate as new areas are explored. T. G. Halle (1914) has described the Permo-Carboniferous glacial beds of the Falkland Is., and proposes the name Lafonian for the series marked by the ancient " tillite " and by Glossopteris.

Regional Stratigraphy. Among the additions to knowledge of the stratigraphy of various lands, the following may be selected as those of most importance.

In the British Isles the former prevalence of the Upper Cretaceous sea has received general recognition. Its deposits were easily re- moved by denudation ; but the discovery of chalk and flints in con- siderable abundance off the W. coast of Ireland (Geol. Surv. Ireland, Mem. on rocks dredged from the Atlantic, 1910) and the tracing of the probable Cenomanian sea-floor across Anglesey and Snowdonia