60 BIOLOGICAL SOCIETY OF WASHIXOTOX. 



this great inland sea from the surrounding land, and that the sea 

 had at least one great outlet, are necessary conclusions. 



Now, the waters of the oceanic belt, which immediately preceded 

 the Laramie sea, contained an abundant marine fauna, a large part 

 of which necessarily died by the subsequent freshening of the waters, 

 and in consequence of this, as we may suppose, many lines of ge- 

 netic descent were broken. The surviving faunas were able to 

 thrive in brackish and fresh waters respectively, both of which, as 

 already stated, the Laramie sea contained. That the brackish- 

 water forms, which survived in the Laramie sea, originated in the 

 estuaries which existed upon its borders, before that sea was cut off 

 from the open ocean, is probable, from the fact that those forms are 

 largely identical in type with certain forms which are known to 

 have existed in the same region just prior to the Laramie period. 

 That the progenitors of the fresh-water Laramie species may have 

 occupied some of the streams which emptied into the sea before it 

 became land-locked is probable, but I regard it as also probable 

 that they originated, at least in large part, in the Laramie sea. 



Accepting the conclusions which have just been expressed, con- 

 cerning the former existence and the character of the Laramie sea, 

 which conclusions I have reached from a biological standpoint, we 

 obtain a remarkably comprehensive view of the conditions which 

 prevailed, during the Laramie period, upon what was destined to 

 be our continent. There rises before the imagination of the investi- 

 gator — an imagination chastened and curbed by a rational interpre- 

 tation of facts — a great continent, whose outlines, it is true, are hid- 

 den in the mists of uncertainty ; but he sees, resting upon its broad 

 surface, an inland sea, the like of which for magnitude the earth has 

 never known before or since. On every side stretches away a broad 

 expanse of comparatively level country ; a few mountains are seen 

 in the distance, but not a peak of the great Rocky Mountain sys- 

 tem has yet arisen. The land is covered with verdure and diversi- 

 fied by forests of wonderful growth ; the busy hum of insects fills 

 the air ; the bright scales of fishes gleam in the waters of the sea ; 



