440 abstracts: geology 



have fossils been found, and their differentiation and correlation is 

 based largely on lithologic and stratigraphic grounds. Younger forma- 

 tions consist of sands and gravels, shales, ligniticbeds of Tertiary age 

 and a great abundance and variety of Quaternary deposits. The pro- 

 ductive gold placer deposits of the district are all in the basins of the 

 streams that head in the Kantishna Hills. A large part of the gold of 

 the stream placer gravels was derived by erosion from the fissure quartz 

 veins that cut the Birch Creek schist. The veins which carry gold, 

 silver, and antimony have been prospected but the inaccessibility of 

 the region has prevented thejr development. R. W. Stone. 



GEOLOGY. — Some American cretaceous fish scales. T. D. A. Cock- 

 ERELL. U. S. Geol. Survey Prof. Paper 120-1. Pp. 165-202, pi. 7. 

 1919. 



Fish remains are extremely abundant in several Cretaceous formations 

 of the Rocky Mountains and Great Plains, but except in the Niobrara 

 formation of Kansas, a fish skeleton well enough preserved for descrip- 

 tion or identification is the greatest rarity. In the original descriptions 

 of both the Mowry and the Aspen shales of Wyoming the presence of 

 fish scales is mentioned as a characteristic feature. 



Descriptions of scales without figures are unsatisfactory, especially 

 if they are to be largely used by stratigraphers who have no intimate 

 knowledge of lepidology. Consequently it has been considered neces- 

 sary to illustrate this paper fully, with enlarged figures, from photo- 

 graphs. 



This discussion deals almost entirely with a marine fauna. So far 

 as known at present the Tertiary fishes mark a considerable advance 

 on or at least change from their Cretaceous predecessors. It ought 

 to be possible as a rule to distinguish a Cretaceous from a Tertiary de- 

 posit by means of a single well-preserved fish scale. The exceptions 

 will be found in those groups which range with little change from the 

 Cretaceous to the present day — the berycoids, clupeids, or hemiramphids. 

 Just as the Tertiary fishes mark an advance on the Mesozoic, so also 

 the later Cretaceous fishes present evidence of evolution and moderniza- 

 tion. This statement applies not only to the Upper as contrasted with 

 the Lower Cretaceous, but also, and rather markedly, to the Montana 

 group as contrasted with the Colorado group. Thus evidence is found 

 of a rather slow and gradual modernization of the fish fauna, the breaks 

 in the series corresponding with the geologic breaks and not being at- 

 tributable to any extraordinary migrations or sudden new develop- 



