HOOSIER EIDGE. 103 



columnar structure. The thickness of the body can be hardly less than 

 five hundred feet, as roughly determined from the widrii of the outcrop on 

 the spur. That it forms so regular a sheet as shown in the section is an 

 assumption based only on analogy from other sheets of porphyry observed 

 in the Silverheels massive It apparently has its greatest thickness at this 

 point, and thins out to the south and east, and in this respect has something 

 of the laccolite form; but there is no evidence of any sudden steepening in 

 the dip of the adjoining strata. On the contrary, the sandstone beds imme- 

 diately overlying it, as shown in the outcrops on the crest of the ridge, have 

 a regular dip eastward of about 10. Only a few hundred feet of sand- 

 - stones and sandy shales separate this from the next succeeding sheet of por-" 

 phyry, which forms the cap of the first prominent shoulder about twelve 

 hundred feet above the pass. This is a blue-gray rock, weathering yellow, 

 of quite distinct habit, having a conchoidal fracture and a tendency to 

 weather into sherdy fragments. It approaches the normal Silverheels Por- 

 phyry, although coarser grained, showing few distinct crystalline ingre- 

 dients when freshly fractured. On its weathered surface, however, fine 

 needles of hornblende are easily distinguishable. 



Beyond another body of sandstone and shales, and a similar though 

 not identical body of porphyry which caps a second shoulder, a body of 

 argillaceous shales of green, red, and purple colors marks what is assumed 

 as the base of the upper division of the Carboniferous group. From these 

 to the main crest of Hoosier ridge are several outcrops of porphyry sheets 

 and intervening gaps of shaly rocks ; among which a bed of dark-blue 

 limestone, about a hundred feet in thickness, stands out prominently on ac- 

 count of its black weathered surface, opposite the head of the north fork 

 of Beaver Creek. From this were obtained the following Coal Measure 

 fossils : 



Athyris subtilita. Bellerophon, (sp. 1). 



Productus cora. FenesteUa, (sp. ?). 



Pleurolomaria, (P. Valvatiformis f). And spines of an Archceoccidaris. 

 Loxomena, (sp. t). 



On the crest of Hoosier ridge are the reddish sandstones which form 

 the passage from the Upper Carboniferous formation into the overlying 



