170 GEOLOGY OF THE EUREKA DISTRICT. 



Fusilina cylindrica. Productus loDgispinus. 



Chonetes verneuiliana. Productus punctatus. 



Productus costatus. Productus semireticulatus. 



Spriug- Hill and the limestone ridge lying on the west side of the Pinto 

 fault form a synclinal fold whose axis is situated on the western side of the 

 high hill east of the toll road. The strata dip away from the Pinto fault 

 into the ridge at high angles, but on the opposite side of the fold they 

 lie more regularly inclined at a much lower angle. The synclinal structure 

 here does not differ essentially from that shown southward along the 

 geological section E-F, atlas sheet xiii. 



On the south side of Conical Hill a fault coincides with a narrow ravine 

 separating it from the next hill to the south. Both the ravine and fault 

 trend to the south and the latter is finally lost beneath the andesites. On 

 this second hill the beds are still in accord with those of Conical Hill and 

 dip westerly, but to the southward of it runs a cross fault connecting the 

 Hoosac fault with the Conical Hill fault. To the south of this cross fault 

 the limestones again dip easterly in conformity with those of Spring Hill. 



A short distance south of this latter fault the geological section E-F, 

 atlas sheet xiii, crosses the Carboniferous rocks lying between the Hoosac 

 and Pinto faults. Tlie entire block of limestones west of the Conical Hill 

 fault dips easterly at aljout 30^. With apparently only a slight break in 

 the strata along this displacement the beds on the east side of the fault-plane 

 still dip easterly at about the same angle followed by a synclinal tVdd, the 

 westerly beds of which attain angles as high as 70° and Ijotli north and 

 south of the cross-section reaching even 80°. Taken as a whole, the Car- 

 ])oniferous rocks included within this block consist of limestone strata more 

 or less arenaceous with interstratified belts of both fine and coarse con- 

 glomerate and carrying from base to summit characteristic Coal-measure 

 species. It is estimated that the Lower Coal-measiu-e beds along the line 

 of this section have a thickness of about 3,400 feet, but it is evident that 

 the base of the series is not reached, and that there are at least 300 or 400 

 feet of beds, and probably more, on New York Hill and Richmond Moun- 

 tain unrepresented here. Measurements of the Lower Coal-measures in the 

 Diamond Range calculated from observed strikes and dips give 3,700 feet 



