382 J. S. DILLER — GEOLOGY OF THE TAYLORVILLE REGION. 



a position given to it either by displacement or an original unconformity. 

 Although the Jurassic system lias been completely overturned and greatly 

 displaced since its deposition, the character of the movements, so far as 

 they have been made out, were not such as to explain its position folded 

 between older strata of different ages, and we are constrained to believe 

 that there is a marked unconformity at the base of the Jura caused by a 

 folding of the strata at the close of the Triassic. 



A general consideration of the character and distribution of Jurassic 

 strata and fossils throws some light upon the ancient geography of the 

 region. Professor Hyatt has shown that in the Jurassic rocks of Taylor- 

 ville the three great subdivisions, namely, lower, middle and upper 

 Jurassic, are represented, and that it contains a larger number of frag- 

 ments of the series of the Jurassic system than any other known locality 

 in the United States. Fragments of the Jurassic system have been recog- 

 nized in Montana, Wyoming and the Great basin, as well as in Cali- 

 fornia. The general scarcity, if not the complete absence, of vertebrate 

 fossils in the Jurassic rocks of Taylorville indicates, according to Professor 

 Hyatt, that the faunas lived at some distance from the shores of the 

 Jurassic continent and in a more exposed oceanic area than those of the 

 Great basin. He announces the fact also that the remains of Oolitic 

 ammonites have been occasionally picked up west of the crest of the 

 Sierra Nevada. It seems evident, therefore, that during a large part, if 

 not the whole, of the Jurassic period the northern Sierra region was be- 

 neath the sea. and that the disturbance at the close of the Trias, although 

 it folded and faulted the rocks, did not produce permanent dry land. 

 The predominance of sandstones with occasional interbedded conglom- 

 erates, however, evidence rather shallow Jurassic seas at Taylorville. 



According to Dr. Dawson, the disturbance at the close of the Triassic 

 in British Columbia produced quite different results. He remarks : ::: 

 " Though much remains to be discovered respecting this post-Triassic 

 epoch of disturbance, it was evidently an important one, and its results 

 were wide-spread in the Cordilleran region. It is quite possible that it 

 was accompanied by or resulted in producing a general elevation of this 

 entire region above the sea level, as no rocks certainly referable to the 

 Jurassic or next succeeding period have yet been distinctly recognized 

 either in British Columbia or in its bordering regions." 



Neocene-Jura Unconformity. — The Johnson grave] is of fluviatile origin. 

 Northeast t>\' mount Jura it reposes unconformably upon the upturned 

 edges of the massive Jurassic and Triassic formations. This uncon- 

 formity is one of the most conspicuous of the region. It represents a 



* Trans. Roy. Soc. of Canada, vol. viii. see. iv, 1890, p. 7. See also paper by «;. F. Becker, Bull. 

 1. Soc. Am., vol.2, 1890, p. 20 



