180 Ttrtiary. 



masses, or in a flue powder, like fine sand, regularly bedded. The 

 color of these beds is white, but the lines of stratifi.-ation are rendered 

 ver_y distinct by the stains produced by the percolation of impure 

 waters; also, by layers of the same ino-redients, differing in their 

 fineness, and by occasional seams of charcoal, in fragments. Thin 

 layers of pebbles are also numerous, even among the strata of the 

 finest materials. The inclined stratification, called diagonal stratifi- 

 cation, is very common, and in many cases is beautifully shown by 

 multitudes of the finest layers of sand, inclined in diff"erent directions. 



He also identified this Group on Chico creek, in the valle}^ of the 

 Sacramento, at the foot of the Hills of the Sierra Nevada, on Carrizo 

 creek, near San Diego, at Williamson's Pass, Los Angelos and San 

 Pedro. Near Monterey it contains a bed of microscopic organisms, 

 50 feet in thickness ; and he supposed it to underlie the alluvium of 

 the Colorado desert. 



He described the Post-pliocene deposits of Montere}-, San Pedro, 

 and San Diego, and showed a comparatively recent elevation of the 

 strata. The low hills around the bases of the mountains in the 

 Colorado desert, and the elevation of the Coast Mountains, he sup- 

 posed to be of the same age, because they are composed in great part 

 of Tertiary strata, thrown into great wave-like flexures, with here and 

 there a granitic axis of limited extent, but with serpentine abundant. 

 In the auriferous regions, a similar serpentine abounds, and has in all 

 cases the aspect of an intrusive rock. The movements which attended 

 the uplift and plication of the Coast Mountains, must have affected 

 the whole western slope of the Sierra Nevada. He expressed the opin- 

 ion that the impregnation of the rocks with gold, and the formation of 

 the Coast Mountains, were nearly synchronous. 



He described, from the Miocene, at Point Lobos, near San Francisco, 

 Scutella interlineata, and from a brown calcareous sandstone at Vol- 

 cano Ridge, Leda subacuta^ now Nuculana subacuta. Pi'of. Agassiz 

 described, from Ocoya creek, at the western base of the Sierra Nevada, 

 Echinorhinus blakei, Scymnus occidentalis, Galeocerdo productus^ 

 Prionodon antiquus, Hemipristis heteropleurus, Carcharodon rectus, 

 Oxyrhnia jolana, O. ticmtila, Lamna clavafa^ and L. ornata. T. A. 

 Conrad described, from the same locality, Natica genicnlata, N. ocoy- 

 ana, B alia j ug ularis , Pleurotovia transmontanum, Sycotypus ocoyanics, 

 Turritella ocoyana, Coins arctatas, Tellina ocoyana, Ileretrix decisa, 

 Pecien nevadensis, P. catiUiformis ; from the San Diego Mission, 

 Cardium modestum, Corbula diegoana, Nucula decisa, Tellina diego- 

 ana, T. congesta, Mactra diegoayia, Narica diegoana, now Vanikoro 



