194 WANLESS— LITHOLOGY OF WHITE RIVER SEDIMENTS. 



appearance small particles of shot. Staurolite as angular, orange to 

 brown grains is almost always present with the garnet. Other min- 

 erals identified in smaller quantities are: Augite (light green grains), 

 rare; pyrite, very rare; hematite, apatite, and amblygonite (lithium 

 phosphate). Other metallic nonmagnetic grains are perhaps cas- 

 siterite, wolframite, or columbite, all of which are common minerals 

 of the pegmatite dikes of the Black Hills. In the coarser sandstones 

 are found small pebbles of quartz-schist, quartz-sericite schist, and 

 garnet-biotite schist, and a few pebbles of very fine-grained slates. 



The evidence of the composition of the sandstones, as to the de- 

 rivation of their material, is in full accord with the evidence of the 

 direction of the channels, which lead away from the central granitic 

 core of the Black Hills. Garnet, staurolite, the various schist peb- 

 bles, and quartz with inclusions point to derivation from the Algon- 

 kian schists and slates of this central core, and the tourmaline, ambly- 

 gonite, and cassiterite (if present) point to derivation from the peg- 

 matite dikes of the same district. The microcline, augite, and apatite 

 are accessory constituents of the sands and may well have had a 

 similar source. 



The channels are evidently of different ages, as shown by their 

 different stratigraphic positions in the accompanying sections, and 

 some horizons seem to be cut by no channels through their whole 

 visible extent. The upper nodular layer is an example of this. 



A sample of the channel sand from the stream bed of Battle 

 Creek, near Keystone, in the center of the Black Hills pre-Cambrian 

 core, and within 5 miles of Harney Peak was collected and examined. 

 It corresponds very closely in mineral composition to the stream- 

 channel sands of the White River, but differs in the proportion of 

 minerals present, and is generally of coarser grain, ''ontaining more 

 garnets which may reach 30 per cent, of the total sand and more 

 schist pebbles. This would be expected, as the stream is flowing 

 through a garnet-mica schist terrane where the sample was collected. 

 This may be regarded as confirmatory evidence of the Black Hills 

 derivation of the material of the channel sandstones. 



Fresh-Water Limestones. 

 At various levels through the Titanotherium and Lower Oreodon 

 beds are thin sheets or lenses of white limestones. These are some- 



