o — 



37G J. S. DILLEK — GEOLOGY OF THE TAYLORVILLE REGION. 



are slates and sandstone with traces of conglomerate. None of these 

 formations have yielded fossils. Some of them arc but little altered. As 

 they lie beneath the Shoo Fly beds at one end and are associated with 

 Silurian slates at the other, they are regarded as probably belonging to 

 the upper Paleozoic 



The Taylorville slates and the Grizzly quaftzites adjoin the Mont- 

 gomery limestone, which is well exposed along Montgomery creek and 

 the crest of Grizzly mountain. In collections made at these two localities 

 by Mr. Curtice. Mr. Paul and myself, Mr. Walcott * identified the follow- 

 ing forms : 



Crinoid stems. Heliolites. 



Stromatopora , sp. (?) Halysites catenulatus. 



Zaphrentis. Orthis, of the type of 0. flabellum. 



Syri7igapora,like S. serpens. Ormoct ras (Siphuncles of) 



According to Mr. Walcott these fossils are undoubtedly Silurian and 

 " Represent the Niagara horizon of the Mississippi valley and Appalachian 

 provinces.'" 



Eruptive Rocks. — A large part of the Taylorville region is occupied by 

 eruptives, of which there is a great variety, not only in chemical composi- 

 tion and degree of crystallization, but also in manner and time of erup- 

 tion. There are at least seventeen distinct masses of various eruptives 

 distributed with considerable regularity throughout the whole region. 



On the northern side of Genesee valley the diorite has greatly altered 

 the Triassic rocks along its contact. It has converted large masses of 

 them into hornfels. Some of the quartz porphyries or porphyrites may 

 he of early Paleozoic eruption. The porphyrite a short distance south- 

 west of Robinson's certainly dates from the Carboniferous, and during 

 the Trias there were great eruptions of basic lavas. Large masses in 

 mount Jura were extruded at the close of the Jurassic, and since the 

 middle Neocene volcanic activity has played an important role in the 

 geology of that region. 



It is evident from what has been said concerning the eruptives of the 

 Taylorville region that igneous activity did not make its first appearance 

 there suddenly in a later geologic period, as we are apt to suppose, but 

 that, as in British Columbia, it began far hack in the Paleozoic and con- 

 tinued with many interruptions almost to the present. f 



♦Report rendered December 8, 1891. 



IS'-.- I i-eology of British Columbia, by George M. Dawson (Geol. Mag., dec. ii, vol. viii, April and 

 May. 1881, p. 17); see also Later Phys. Geol. oi the Rocky Mountain Region of Canada, with special 

 reference to changes of elevation and the history of the Glacial Period (Trans. Roy. Soc. of Canada, 

 vol. viii, sec. -i. lN'.m. p. 6) by the same author. 



