362 University of California Publications in Geology [Vol. 13 



of the San Gorgonio Quadrangle. Clark 11 has amplified this descrip- 

 tion. The total thickness of the series is 1280 feet, the upper half 

 being Carboniferous limestone, the next 120 feet, middle Cambrian 

 shale, and the lower portion, lower Cambrian limestone, shale, and 

 quartzite. The assignment of the sediments to their respective ages 

 is supported by characteristic fossils. It is a noteworthy fact that 

 no Ordovician, Silurian, nor Devonian rocks are included in the sec- 

 tion and that there is no pronounced unconformity between the upper 

 Cambrian and the Carboniferous. 



Noble 12 has found limestone in the San Gabriel Mountains to the 

 west. He says: 



A very characteristic feature of the granite and gneissoid-granite belt is the 

 presence of bodies of white, crystalline, metamorphie limestone Seem- 

 ingly they are inclusions which have sunk down into the granite. In one of the 

 limestone bodies a few poorly preserved gastropods were obtained which resem- 

 ble forms found in the Ordovician Pogonip limestone of eastern California. The 

 limestone bodies are to all appearances the same rock as the metamorphie lime- 

 stones associated with granite in the neighboring Tehachapi and San Bernardino 

 ranges. 



With these facts before us the problem is to assign the old sedi- 

 ments of the San Bernardino Mountains to their proper places in the 

 geologic column. From Noble's account it would seem most likely 

 that at least part of the Furnace limestone is Ordovician. Part of it 

 may also be Cambrian corresponding to that in Inyo County described 

 by Walcott and to that in the Iron Mountains described by Clark. 

 Then the Arrastre quartzite might well be considered as Cambrian, 

 probably lower Cambrian. If Hershey is right in assigning the quartz- 

 ite of Oro Grande to the Cambrian, this correlation receives further 

 justification. Also, Clark reports Cambrian from the Iron Mountains. 

 That the conditions existing in this region in Cambrian time pre- 

 vailed over an extensive area is further shown in Arizona. Noble 13 

 describes 285 feet of sandstone at the base of the Cambrian in the 

 Grand Canon section. Above this lies about 300 feet of shales and 

 450 feet of limestone, also of Cambrian age. At Bisbee, 14 near the 

 Mexican border, there is a similar section. At the base lies the Bolsa 



11 Clark, C. W., Lower and Middle Cambrian faunas from the Mojave Desert, 

 Bull. Dept. Geol., Univ. of Calif., vol. 13, pp. 1-7. 



!- Noble, L. F., Personal communication to B. E. Dickerson, September 8, 

 1917. 



13 Noble, L. F., The Shinumo Quadrangle, Grand Canyon District, Arizona, 

 U. S. G. S., Bull. 549. 



Bansome, F. L., Geology and ore deposits of the Bisbee Quadrangle, Ari- 

 zona, U. S. G. S., Professional paper no. 21. 



