682 REPORT— 1895. 



their hardness is, speaking broadly, proportionate to their antiquity. The removal 

 of the soluble cement by rain-water causes the rock to crumble, and the bad lands 

 are examples of atmospheric erosion on a very grand scale. This erosion is 

 extremely slow, the soil shedding the rain almost completely, but land-slips and 

 snow avalanches in the spring frequently expose fresh surfaces of rock. The John 

 Day beds are largely composed of the glassy particles of volcanic ash and the whole 

 is overlaid by late basaltic flows. 



In the lake basins the old shore lines and deltas may frequently be traced, and 

 their fossil contents sometimes afford interesting hints as to the habitat of the land 

 animals. 



Climatic changes are registered in the alteration of the floras, as in the gradual 

 disappearance of the palms from the central latitudes and in the diminution in the 

 abundance and variety of the reptiles. For example, large crocodiles are exceed- 

 ingly common in all the Eocene formations, including the Uinta, but in the 

 succeeding White lliver only a few dwarf forms have been found. 



III. The correlation of formations in different continents is a difficult matter, 

 but least so, perhaps, in the case of lacustrine beds in coiviected areas. The Old 

 and New Worlds were certainly so connected during much, if not all, of Tertiary 

 time, and there is always a certain proportion of land mammals common to the 

 two continents. The natural and sharply marked lines of division are, however, 

 not the same, and vpere the American formations arranged without reference to 

 those of any other continent, a system very different from the European would re- 

 sult. Thus the Puerco would form one group; the Wasatch a second; the 

 Bridger, White River, and John Day a third ; the Loup Fork and Blanco a fourth ; 

 and the Equus beds a fifth. 



The European system is, however, the standard, and must be employed, and 

 even in this way some very close correspondences may be noted. Thus, the 

 Puerco is somewhat older than the Ceruaysian, while the Wasatch is the exact 

 equivalent of the Suessonian. The Bridger is Middle Eocene (Parisian or Lute- 

 tian), and the Uinta in a general way corresponds to the I'aris gypsum. The 

 White lliver is Oligocene (Ronzon), and much misunderstanding has come from 

 calling it Miocene. The John Day may be placed in the Lower Miocene, though it 

 is somewhat older than the bed's at St. t.T6raud-le-Puy, and follows the White 

 River epoch with hardly a break. 



None of the American lacustrines is referable to the Middle Miocene. The 

 Loup Fork is Upper Miocene, the Deep River division corresponding almost exactly 

 to the beds of Sausan and Steinheira, while the Palo Duro division is perhaps 

 already basal Pliocene. The fauna of the Blanco series is not yet sufficiently well 

 known for exact correlation, though there can be no doubt that it is Pliocene. 



The Equus beds are distinctly Pleistocene, though it still remains to trace their 

 relations to the Drift and to determine whether they are pre-Glacial or Glacial. 



4. The Glacial Age in Tropical America. By R. Blake White. 



The deposits described by the author cover almost the whole of the Republic 

 of Colombia, extending from 12° N. lat. nearly to tlie Equator, and from the 

 summits and plateaux of the Andes at 10,000 and 12,000 feet down to the plains, 

 valleys, and littorals of the Atlantic and Pacific Oceans. The Glacial age corre- 

 sponded, in his opinion, with tliat of greatest volcanic activity. He speaks of 

 moraines from 2,000 to 3,000 feet thick, accumulation of boulders, erratics of 

 enormous size, and a peculiar loess on the high lands, the last containing bi- 

 pyramidal crystals of quartz supposed to have been formed in situ. Great 

 denudation followed the melting of the ice, and the auriferous deposits of the 

 country belong to this or to the Glacial age. The author considers that a decrease 

 in temperature enough to bring the snow line from 2,000 to .3,000 feet lower than 

 it is at present would account for the phenomena which he describes. This might 

 be brought about by a diminution of the amount of carbonic acid in the atmosphere, 



