168 GEOLOGY OF THE EUEEKA DISTRICT. 



Feet. 



9. Cherty bluish gray limestone, cairyiug Grijfithidc.s 2)<»'tlocl-i, ryoductun 



scmiretieidafus, I', loiigispinux, P. pratlcmanuti, FunUina cylindrica. . . 300 



10. Blue limestones in massive layers, with thin iuterbedded calcareous shales 



carrying Pleurotomaria conoidea, Metoptomia peroccidens, Macro- 

 cheilus, Ifucula, Orthocerus, Leperditia 400 



11. Dark argillaceous shales, weathering to blue and gray clays, carrying 



fresh water shells and plant remains Unknown thickness. 



1, 5l>5 

 Throughout the eutu-e series of beds above the quartzite band (No. S) 

 occurs a g-roupiug of characteristic Coal-measure fossils from which 

 twenty-eight species have been determined. The list will be found in the 

 chapter devoted to the Carboniferous rocks. Overlying the limestones the 

 andesitic rocks rise in precipitous walls for over 800 feet. 



spring Hill.— The Uppermost members of the Richmond Mountain beds 

 are traceable across Eureka Canyon, the conglomerates standing out 

 conspicuously along the west slope of Spring Hill dipping into the 

 ridge. A line of displacement runs along the Secret Canyon Road valley, 

 and, as it approaches the Hoosac fault, the continuity of strata becomes 

 more and more difficult to follow, showing signs of displacement under the 

 influence of the outpouring of lavas near the centers of volcanic activity 

 About a mile up the valley a complete change in structure takes place and 

 a low hill, somewliat isolated from the ridge, stands out between the main 

 body of Spring Hill and the Hoosac fault. It rises about 400 feet 

 above the level of Secret Canyon Road and from its peculiar outlines, the 

 result of erosion, it has been designated as Conical Hill. It presents a 

 small block of Lower Coal-measure strata which, instead of di])ping easterly 

 in conformity with the rest of Spring Hill, forms an anticline with 

 the main ridge, the beds dipping westerly directlv toward the Hoosac 

 fault. On Conical Hill the strata strike from N. 20°-25° E., parallel with 

 the Canyon Road valley, and dip 30^ W.^ On both sides of the axis of 

 the fold the series of beds are easily traced, consisting of limestones, cal- 

 careous shales, arenaceous layers, with a well defined bed of coarse con- 

 glomerate about 75 feet in thickness. This conglomerate appears on the 



' Owiug to an error in the proof-reading of tlio map, the beds on Conical Hill are represented as 

 inclined steeply to the east, whereas the dip of 30- to the west, as given in the text, is correct. 



