198 IRVING. 



series. Newton divided it into a newer or Eastern series of 

 slates and an older or Western series of schists, which he cor- 

 related with the Huronian and Laurentian respectively. Car- 

 penter and Crosby have sustained this division, but the latter 

 authority correlated the rocks with the Archean of New Eng- 

 land. 



Van Hise ^ studied the district in 1889 and stated it as his 

 belief that no division into two unconformable series could be 

 established. He attributes the more thoroughly crystalline 

 character of the schists of the Western series to the metamorphic 

 action of the intruded granite. He then mentions an area of 

 garnetiferous schists about Deadwood and shows that the 

 slates there pass insensibly into schists. The intruded rocks 

 of the northern hills he considers as the agents that have meta- 

 poosed portions of the slate area into crystalline schists. Al- 

 though the writer has not seen the schists of the southern hills, he 

 has examined carefully the schistose area between Deadwood and 

 Central City and cannot agree with Van Hise that these schists are 

 the result of contact metamorphism. The slates do unqestion- 

 ably grade into schists as we descend Deadwood gulch beyond 

 Central City, but it is especially in these schists that dikes are 

 noticeably rare. On the other hand in those portions of the 

 Algonkian area, such as the region around Texana, and in the 

 vicinity of Terry, where the eruptives are in enormous develop- 

 ment, the Algonkian rocks are preeminently argillaceous slates 

 and phyllites. These schistose areas must then be attributed 

 to the locally greater strength of the same metamorphic agencies 

 that have altered the entire Algonkian series, rather than to the 

 influence of intrusives. 



2. Cambro- Silurian. 



A complete section of rocks forming the Cambrian was not 

 obtained at any one locality. In the canon of Spearfish creek 

 the lower strata were found quite well exposed, but the upper 



1 C. R. Van Hise, The Pre-Cambrian Rocks of the Black Hills. Bull. Gcol. 

 Soc. of America, I, 203, 1890. 



