SPRING HILL. 169 



west siile of Conical Hill ami again near the summit of Spring Plill, 

 standing- out prominently on Ijotli sides of the fault as a well defined body, 

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

 The transition from the calcareous to the siliceous beds is I'apid, both above 

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

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

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

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

 but most tvpical Coal-measure fauna. xibove these shaly beds, al)out "JOO 

 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 l)elt of fine conglomvi'ate 

 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 Sj^ring Hill. It crosses the canyon near the toll-house, with a strike 

 of N. 1G° 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 Spirifcra liiicata and a small 

 Discina not unlike D. m'nmta. This shale varies somewhat in thickness, but 

 was estimated at 50 feet. The origin of the canyon is in pai;t 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 Avith nearly all the other 

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

 sembles Secret Canyon. Overlying the conglomerates l)lue and gra}- lime- 

 stones ccmtinue on up to the sinnmit of the section, with occasional thin 

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

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

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

 about 100 feet below the suunint, there were collected : 



