1921] Clark: Lower and Middle Cambrian Formations 



7 



CORRELATION 



The Cambrian section of the Mojave Desert may possibly be 

 correlated with the Cambrian of central and eastern Nevada. Accord- 

 ing to WaWcott, 8 Olenelhis is found in a thin bed of shale lying just 

 above a massive quartzite in several localities in Nevada, notably in 

 the Eureka District, in the Highland Range, and also in the Big Cot- 

 tonwood section of Utah. This shale is near the top of the Lower 

 Cambrian in the localities just mentioned and in the Mojave region 

 it appears to have a similar position. 



The Lower Cambrian quartzite in Bristol Mountain rests on an 

 erosional surface of pre-Cambrian granite. In many of the sections 

 of the Great Basin containing Cambrian sediments, the bottom of the 

 sedimentary series is not exposed, but, according to Hershey, 7 the 

 Lower Cumbrian just west of Clover Valley in eastern Nevada rests 

 on pre-Cambrian granite and schists. Spurr 8 thinks that probably 

 much of the Cambrian in northeastern Nevada is underlain by pre- 

 Cambrian igneous rocks. However, he states that some granites which 

 have been supposed to be pre-Cambrian have upon investigation 

 been proved to be later intrusives. In the Mojave Desert region these 

 later or post-Carboniferous granites are abundant and have been the 

 principal cause of the metamorphism, but the pre-Cambrian granites 

 and schists occur in large areas and are cut by the later granite. 



The writer is indebted to Dr. C. D. Walcott for very kindly review- 

 ing the manuscript of this paper. 



e U. S. Geol. Surv. Bull. No. 81, 1891. 



' Am. Jour. Sci. Ser. 4, vol. 34, p. 267, 1912. 



s IT. S. Geol. Surv. Bull. No. 208, p. 27, 1903. 



