. 3fesozoic and GcEnozoic Geology and Palwontology. 207 



sandstones, without any appearance of eruptive rock, and also with 

 very little metaniorphism. 



The unaltered sandstones extending along the Gavilian Range, near 

 the San Juan valley, and forming the San Juan hills, which extend to 

 the Pajaro river, are referred to the Miocene. In these hills the strata 

 are very heavy bedded, and have a dip everywhere to the south. The 

 materials of which they are made up are often coarse, and sometimes 

 large enough to form a conglomerate, among the pebbles of which jas- 

 per and other metamorphic rocks predominate. 



In the vicinity of the Ba}- of Monterey the granite is flanked bj* Mi- 

 ocene sandstone. Both rocks are considerably'' altered, for a distance 

 of about 20 feet from the junction; the sandstone is softened and dis- 

 integrated, and the granite discolored. The metamorphism has so af- 

 fected both rocks that it is not easy to determine the exact line of 

 junction. 



The Miocene sandstones are displayed in some places in the region 

 between the Canada de las Uvas and Soledad Pass, nearly 2,500 feet 

 in thickness. From the summit of the higher upturned strata, a wide 

 belt of Tertiary rocks may be seen skirting the Coast Ranges, and 

 worn into rounded hills, which are generally barren, especially on the 

 west side of the Tulare valley. 



The Pliocene beds between Merced Lake and Mussel Point, on the 

 peninsula of San Francisco, are made up of a bluish sandstone, of 

 which the grains are cemented by carbonate of lime, interstratified with 

 hard, fine conglomerates, of which the pebbles are evidently derived 

 from the adjacent jaspery rocks of Cretaceous age. These strata con- 

 tain Scutella interlineata, Crepidula princeps, both of which are ex- 

 tinct, together with several species still living on the coast. 



At the head of Pleasant valley, the strata are overlaid by beds of 

 volcanic ashes, interstratified with gravels, the whole series being con- 

 formable and dipping at a low angle to the east. They appear to be of 

 Pliocene age, and identical in most respects with the sedimentary vol- 

 canic beds to the north of Kirker's Pass. 



To the north of San Pablo are low hills of very recent strata, which 

 are nearly horizontal, and which rest unconformably on the edges of 

 the Tertiar3^ They are referred to Post-pliocene age. 



From Tres Piuos, 13 miles from San Juan, to Booker's, a distance of 

 about 13 miles in a direct line, the road follows the Arroyo Joaquim 

 Soto, a branch of the San Benito. Along this road thei'e are vast de- 

 posits of gravel, or entirely unconsolidated detritus, and which form a 



