HOOSIER PASS SECTION. 101 



the Archean, witli the exception of a thin rim of Cambrian quartzite around 

 its upper walls, and was probably carved out by a tributary of the main 

 Blue River glacier, which descended the gorge from the back of Quandary 

 Peak. 



A section was made from this saddle eastward across Hoosier pass 

 to Hoosier Ridge, which connects the Silverheels massive with the group 

 of hills to the north that constitute the eastern boundary of the Blue River 

 Valley. This ridge also forms the divide between the waters of the Blue 

 and Upper Platte Rivers and those of Tarryall Creek. 



No satisfactory measurements could be obtained of the thickness of 

 the members of the Carboniferous group above the Blue Limestone, as was 

 hoped: first, because the line followed did not cross the strata at right 

 angles, but at times almost followe d the strike ; secondly, because of the 

 great number of beds of porphyrj' included in the section, whose thick- 

 ness could not be determined ; and, thirdly, because of the evidence of a 

 syncline on Hoosier pass itself. Nevertheless, the data obtained are given 

 here somewhat in detail, as it was one of the few opportunities offered during 

 the investigation to follow continuously the ascending series of beds from 

 the Blue Limestone up to the assumed top of the Carboniferous formation. 



From the saddle eastward to the grass-covered sunmiit of the pass the 

 outcrops may be assumed to indicate a thickness of about two thousand 

 feet of beds. In this are included those of two prominent sheets of porphyry, 

 which are apparently interbedded. On the first hill east of the saddle is an 

 outcrop of shales, containing indistinct casts of fossils, apparently Zaphrentis 

 and corals, which probably form part of the Weber Shales. The other 

 outcrops are of the characteristic gritty rocks of this series (either micaceous, 

 quartzose schists or coarse white sandstone, rich in muscovite and often 

 passing into conglomerate) and one bed of black argillaceous shale, which all 

 show a conformable dip to the east and north. The grass-grown glades 

 which form the summit of the pass leave a gap about half a mile without 

 outcrops. Towards the eastern side, and overlooking the liead of Blue 

 River, a prospect shaft on the Ready- Pay claim has cut a body of light- 

 gray limestone, which is probably one of the thin beds of limestone found 

 in the middle of the Weber Grits series. This limestone, as well as an 



