1 882.] Central Region of the United States. 179 



menced. Extensive lakes were formed in the depressions of the 

 Laramie and older beds which formed the surface, which were 

 probably connected over a tract extending from near the Missouri 

 river to Eastern Wyoming and Colorado. Near the same time a 

 similar body of fresh water occupied a large part of what is now 

 Central Oregon and certain areas in Northwestern Nevada, accord- 

 ing to King. The sediments now deposited constitute the White 

 River formation, and the faunal distinctions which I have discov- 

 ered to characterize the eastern and western basins have led me 

 to employ for them the subdivisional names of White River beds 

 for the former and Truckee (King) for the latter. It may have 

 been during the early part of this period, or during the Uinta, 

 that there existed two contemporary bodies of water, separated 

 by a wide interval of territory. One of these extended over a 

 considerable tract in Northern Nevada, and deposited a coal bed 

 near Osino. A formation probably the same, has been found by 

 Professor Condon in Central Oregon, underlying the Truckee 

 Miocene beds. The other lake left its sediments near Florissant, 

 in the south park of Colorado. This formation I have named 

 the Amyzon beds, 1 from a characteristic genus of fishes which is 

 found in it. It has been referred to the Green River formation 

 by King, but in contradiction to the present palaeontological evi- 

 dence, as it appears to me. 



The oscillations of the surface which brought the White River 

 period to a close, are not well understood. Suffice it to say here, 

 that after an interval of time another series of lakes was formed, 

 which have left their deposits at intervals over a wider extent of 

 the continent than have those of any other epoch. These con- 

 stitute the beds of the Loup Fork period, which are found at 

 many points between the Sierra Nevada and the Rocky moun- 

 tains, from Oregon to New Mexico, and over parts of the Great 

 Plains of Colorado, Kansas, and northward, and in the valleys of 

 the Rocky mountains. King has shown that the beds of this 

 epoch are slightly elevated to the westward, thus proving that 

 the elevation of the Rocky mountains had not entirely ceased at 

 that late day. A probably continuous succession of lakes has 

 existed from this period to the present time in ever-diminishing 

 numbers. The most important of these later lakes were in the 

 Great basin in Oregon, in Washington and in Nebraska, and their 

 'American NATURALiiT, May, 1879. 



