GEOLOGICAL SURVEY OF THE TERRITORIES. 431 



described by Dr. Leidy as Clupea humilis, (Proc. Acad. !Nat. Sei., Pkila., 

 1856, p. 256.) One of the blocks contains the remains of two small 

 slioals of the fry, probably of C. humilis, which were caught suddenly 

 by a slide or fall of calcareous mud, and entombed for the observation 

 of future students. They must have been taken unawares, since they 

 lie with their heads all in one direction as they swam in close bodies, 

 One or two may have had a moment's warning of the catastrophe, as 

 they have turned a little aside, but they are the exceptions. The fry 

 are from one-half to three-quarters of an inch long and upward. 



True herring, or those with teeth, are chiefly marine, but they run 

 into fresh waters and deposit their spawn in the spring of the year, and 

 then return to salt waters. The young run down to the sea in autumn 

 and remain there till old enough to spawn. The size of the fry of the 

 Eocky Mountain herring indicates that they had not long left the 

 spawning ground, while the abundance of adults suggests they were not 

 far from salt water, their native element. To believe, then, that the 

 locality from which these specimens were taken was neither far from 

 fresh, nor far from salt waters, is reasonable ; and this points to a tide, 

 or brackish inlet or river. The species of Cyprinodontidce inhabit also 

 tide and brackish waters. Most of the species of the family, as well as 

 of the genus, are inhabitants of fresh water ; but they generally, espe- 

 cially the cyprinodons proper, prefer still and muddy localities, and 

 often occur in water really salt. This habitat distinguishes them espe- 

 cially from Cyprinidce (minnows and suckers) and pike. Lastly, the 

 known species of Osteoglossum inhabit fresh waters. 



The material which composes the shales indicates quiet water, and 

 not suck as is usually selected by herring for spawning in ; while the 

 abundance of adult clupeas indicate the proximity of salt water. 



This is far from a satisfactory demonstration of the nature of the 

 water which deposited this mass of shales, but is the best that can be 

 obtained with such a meager representation of species. 



As to geological age the indications are rather more satisfactory. 

 The genus Clupea ranges from the upper eocene upward, being 

 abundant in the slates of Lebanon and Monte Bolca, while Cyprinodon 

 has been found in neither, but first appears in the middle or lower 

 miocene in Europe. The Asineops resemble very closely, and I believe 

 essentially, the Pygseus of Agassiz of eocene age, from Monte Bolca. 

 The peculiarities presented by the genus found by Dr. Hayden are of 

 such small significance as to lead me to doubt the beds in question being 

 of later than eocene age, though the evidence rests chiefly on this 

 single, new, and peculiar genus. 



The position of these fishes, seven thousand feet above the level of 

 the sea, furnishes another illustration of the extent of elevations of 

 regions once connected with the ocean, and the comparatively late 

 period of geologic time at which, in this case, this elevation took place. 



