TRANSACTIONS OF SECTION C. G47 



these agencies the impoverishment of the atmosphere was hastened, and the epoch 

 of cold precipitated. 



But when glaciation spread over the crystalline areas whose alterations were 

 the chief source of depletion, the abstraction of the carbonic acid was checked, and 

 if the supply continued, the re-enrichment would begin and warmth return. With 

 returning warmth the ocean would give up its carbonic acid more freely, and the 

 accumulated vegetable matter would decay, adding its contribution of carbonic 

 acid and accelerating the re-enrichment of the atmosphere. But when again the 

 ice disappeared and the ci-ystalline areas were exposed to alterations the depletion 

 would be renewed, and so the rhythmical movement would continue until the land 

 was lowered or the general conditions changed. 



2. Distribution and Succession of the Pleistocene Ice Sheets of j\'ortheno 

 United States. By T. C. Ciiambeelin, Professor of Geology in the 

 University of Chicago. 



In this communication the author presented a synopsis of the leading events in 

 the history of the Pleistocene as determined from studies of Glacial deposits 

 throughout. Northern United States from the Rocky Mountains to the Atlantic 

 Coast, and from the mouth of the Ohio northward to the Canadian border. The 

 several ice sheets determined from their products were defined, and the extent of 

 each was indicated ; while the eti'ect of Glacial action on topographic configuration 

 and the geographic features of the country was developed. 



3. On the Glacial Formations of the Alps. By Professor A. Penck.' 



The former glaciation of the Alps resembled very much that of British Colum- 

 bia and Alaska of to-day. The valleys were tilled with glaciers, which poured into 

 the Piedmont region, forming here large ice-lobes. The borders of these ice-lobes 

 are formed by terminal moraines ; in the interior occur drumlins with a radial 

 direction, and depressions filled with water forming lakes, or with alluvial deposits 

 forming peat-mosses or gravel-flats. 



The glacial formations consist of true moraines and fluvioglacial deposits. Three 

 different formations of this kind can be distinguished, the older beingweathered below 

 the younger. Judging from the thickness of the decomposed parts, the relation of 

 the duration of the postglacial and the two interglacial epochs may be estimated as 

 1:4:6. The duration of the postglacial time cannot have been less than 20,000 

 years ; the duration of both interglacial epochs, therefore, appears to have exceeded 

 200,000 years ; the total length of the great ice age, with its glacial and interglacial 

 epochs was, judged by the deposits of the Po plain, 500,000 years. Interglacial 

 sections prove that in the interglacial epochs the glaciers retired to the remote 

 corners of the mountains. The loess is the characteristic formation of the Alpine 

 interglacial epochs. Its development is in favour of Baron v. Richthofen's teolian 

 hypothesis, for the loess is confined to ilie central European districts of the Alps, 

 and is wanting in the Mediterranean climate. But it is also probable that the 

 material of the loess is of fluvioglacial origin. The older glacial deposits of the 

 Alps have experienced a slight folding ; parallel to the strike of the Western Alps 

 they describe a succession of synclines and anticlines. 



All Alpine lakes lie within the limits of the last glaciation ; their origin, how- 

 ever, is a very complex one. They are, in general, deformed valleys, deepened and 

 widened by the ice, and dammed by its moraines. 



The postglacial epoch appears short in comparison with the interglacial epochs, 

 and if there occurred times of readvance of the ice, which are probably indicated by 

 terminal moraines in the valleys, they were less than the three glacial epochs. 

 There is abundant evidence for the existence of man during the last glacial and 

 the last interglacial epoch ; its antiquity in Europe can be estimated as about 

 150,000 years. 



' The paper will be published in the Journ. of Geology, Chicago. 



