2 University of California Publications in Geology [Vol. 13 



Bristol Mountain is a long, low range of hills or ridges composed 

 of igneous and sedimentary rocks representing various geologic ages. 

 The sediments range in age from Lower Cambrian to Carboniferous. 

 The mountain is about 20 miles long and from 1 to 3 miles wide, the 

 highest peaks reaching an elevation of 1000 to 1300 feet above the 

 desert plain. It is situated on the north side of a great dry lake basin, 

 the lowest point of which is near the town of Amboy. Just south of this 

 town there are extensive beds of salt and gypsum which were left as 

 a deposit when the lake became dry. How large this lake was is not 

 known, but the country slopes toward the saline deposit for many 

 miles on all sides except the southeast. 



Sedimentary rocks very similar to those in Bristol Mountain are 

 present in a number of other ranges in this region, but most of them 

 have suffered more intense metamorphism. The character of the sedi- 

 ments and the fauna contained in them indicate that these formations 

 may be correlated with those described by Darton in the Providence 

 Range to the north and also with those of the Highland Range in 

 Nevada. The Providence Range was not visited owing to the limited 

 time allotted to the work. The study of the section in Bristol Moun- 

 tain, together with more detailed collecting in other exposures of 

 sedimentary rocks in this region, should add many facts to our 

 knowledge of the Paleozoic of the Great Basin. 



OCCURRENCE OF FORMATIONS 



The writer has visited localities in the Ship Mountains, the Marble 

 Mountains, and the Clipper Mountains, but no fossils were found 

 in these ranges. All the fossils referred to in this paper were 

 obtained in Bristol Mountain. Paleozoic strata occur at two localities 

 in this range. At the southern end their exposure extends to the north- 

 west for about two miles to a point where they have been entirely 

 stripped from the underlying granite by erosion. From this point 

 granite and Tertiary lavas make up the range, forming low rounded 

 hills for three or four miles toward the northwest to a point where the 

 granite is again overlain by Cambrian strata. Here the exposure of 

 Paleozoic rocks begins just north of a deep canon which transects the 

 range. The rocks extend toward the northwest overlying the pre- 

 Cambrian granite for a distance of about three miles, beyond which 

 they have been cut off abruptly by a large post-Carboniferous granitic 

 mass. Although the range was not visited farther north, the writer 

 was informed by a resident of the district that the whole of the northern 

 end is composed of igneous rock. 



