•48 COLORADO COLLEGE STUDIES. 



son at Austin. If Ostrca quadriiplicata extends up into the 

 Grayson terrane, or beyond the basal transitional part of it, 

 such occurrence is certainly rare. 



A few of the species now apparently confined to one of 

 these terranes, will doubtless be found, sooner or later in the 

 other; but, even so, many of the forms that occur in both are 

 extremely rare in one while common in, and so, in a sense, 

 characteristic of the other; and it is obvious that the faunal 

 aspects of the two terranes, like the lithological, are — and are 

 likely to remain — far more conspicuous for their differences 

 than for their resemblances. 



