TUIO POTSDAM IN DETAIL 1J<) 



the schists, but few and very inij)erfect exposures were seen of the Potsdam, 

 which was usually found on the slopes only in fra^^ments or in narrow and 

 broken outcrops Near the junction of Castle and Slate Creeks, however, 

 the base of the formation was seen to be composed of 75 feet of coarse 

 sandstone, its lower part being a coarse conglomerate of quartz pebbles, 

 while above it for 200 feet fragments of coarse yellow or brown sandstone, 

 sometimes calcareous and containing grains of glauconite, were seen scat- 

 tered over the slope. These are succeeded by small outcrops of the shaly 

 lower member of the Carboniferous, with crinoidal fragments, Prodiidus, 

 etc., and then comes the Carboniferous limestone, forming a clift' of 150 

 feet, the rampart of the valley. The metamorphic rocks, here cut to a 

 depth of 1 50 feet by the creek, consist of micaceous, talcose, and chloritic 

 schists, dipping 80° to 85° west, with a strike nearly northwest and south- 

 east, while the sedimentary rocks above appear to be almost horizontal. 



A few miles south of this point on Slate Creek the following section 

 was observed by Mr. Jenney: 



Carboniferous. 



Feet. 

 8. White, pinkish, and grayish silicious limestone, with Spirifera earner ata, Fro- 



ductus^ etc 100 



7. White compact limestone, containing the same fossils 100 



6. Unexposed slope 250 



Potsdam. 



5. Soft brown sandstone containing abundant fossils, Lingtilepis, Obolella and trilo- 



bite fragments 50 



4. Coarse grained, brownish yellow sandstone, with small quartz pebbles, merg- 

 ing into bed 3 50 



3. Conglomerate of quartz bowlders and pebbles, cemented by sand and oxide of 



ii'ou, with some lime 55 



2. Unexi)osed slope 35 



Archa;an. 

 1. Chloritic, talcose, and mica schists; dip, 55° west; strike, north to northwest. 



Some five miles southeast from this section a rounded peak, which is 

 locally a prominent landmark, was found to contain a small but very fossil- 



