SPRING HILL. 169 



west side of Conical Hill and again near the summit of Spring Hill, 

 standing out prominently on both sides of the fault as a well denned body, 

 serving as an excellent datum ledge in determining the position of the beds. 

 The transition from the calcareous to the siliceous beds is rapid, both above 

 and below the conglomerate. This description of Conical Hill is given 

 somewhat in detail, as it is here that the Lamellibranchiate fauna of the 

 Carboniferous occurs. On the east slope of this hill, near the saddle which 

 connects it with Spring Hill, there is found in a shaly limestone a small 

 but most typical Coal-measure fauna. Above these shaly beds, about 200 

 or 300 feet, occur the limestones carrying the Lamellibranchiate fauna, asso- 

 ciated with Coal-measure species, as described in the chapter on Carbon- 

 iferous rocks. Ovei lying the Lamellibranchiate beds, on the east side of 

 the fold, on the east side of Spring Hill, characteristic Coal-measure fossils 

 come in, but without the mingling of the fauna found below. 



These limestones are in turn overlain by a belt of fine conglomerate 

 100 feet in thickness, in places altered to an indurated sandstone, which 

 forms the lower slope of the ridge on the west side of Eureka Canyon south 

 of Spring Hill. It crosses the canyon near the toll-house, with a strike 

 of N. 16 E. and is traceable on the opposite hills without difficulty. At 

 the east base of Spring Hill, along the bottom of the Eureka Canyon 

 and underlying these conglomerates, occurs a thin band of black, fissile, 

 argillaceous shale, from which were collected Spirifera lineata and a small 

 Discina not unlike D. minuta. This shale varies somewhat in thickness, but 

 was estimated at 50 feet. The origin of the canyon is in part due to a 

 fracture in the quartzite and in part to the nature of the easily eroded 

 shales, but it does not appear to be accompanied by any considerable 

 amount of displacement of strata, as is the case with nearly all the other 

 principal longitudinal drainage channels; in this respect, however, it re- 

 sembles Secret Canyon. Overlying the conglomerates blue and gray lime- 

 stones continue on up to the summit of the section, with occasional thin 

 bands of chert and arenaceous layers, but with less and less siliceous mate- 

 rial. On the top of the ridge east of the toll-house the gray limestones 

 carry a typical Coal-measure fauna, and in a thin bed on the west side, 

 about 100 feet below the summit, there were collected: 



