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from La Brae to the Llagos Creek ; after which they are not again seen 

 for several miles. Near the last named creek, the more recent volcanic 

 rocks make their appearance and continue, at short intervals, for sixteen 

 miles, when we again pass into the primitive formations, which become 

 more metaliferous and particularly in the region about New Almaden in 

 the county of Santa Clara, 



North of Almaden, and near the Los Gatos Creek, a bed of recent con 

 glomerate, loose and friable in texture, is found occupying an elevation of 

 four hundred feet above the level of the valley, and having a thickness of 

 about seventy feet, it occurs on both sides of the Los Gatos, and is found, 

 at short intervals, for ten miles, crossing Camels Creek and following its 

 banks for two or three miles ; it has been considerably disturbed and large 

 masses have been thrown down. West of McCartyville the mountain 

 limestone occurs in large masses and is continuous for several miles to the 

 west, north and north-west. Extensive operations are now conducted in 

 the manufacture of lime for the market, for which purpose it is admirably 

 adapted. This group of calcareous rocks cannot be less than thirty miles 

 in length from east to west, and has a strike transverse to the line of the 

 mountain range, appearing on the coast at Santa Cruz, at this point it is 

 highly crystaline. These rocks extend north of Camel's Creek about 

 four miles ; and a calcareous rock of an amorphous character is found as 

 far north as Sanchez Eanch, in the County of San Francisco. The west 

 flank of the mountains, lying between the San Mateo and a point nearly 

 west of Mission Dolores, was not examined personally, but from the spe 

 cimens of rocks from that section, which I have seen, their geological cha 

 racters appear identical with the rocks at the Presidio, which are mostly 

 serpentine. 



On Presidio point are to be found beds of a Jaspery rock having a 

 riband-like appearance, and colors from a greenish hue through red- 

 brown to red and yellow ; this rock has been considered by Mr. Dana as 

 a variety of the Prasoid rocks, and as he says "the graduation of prase 

 into jaspery rocks exhibits a close relation of both." These transitions 

 were met with in other parts of the country over which he had travelled. 

 In relation to this subject he further says "From the transitions that 

 occur, it also appears that the jasper and prase rocks are closely connected 

 with the talcose series, and that the translucent jasper and bloodstones of 

 this section are only different varieties of its condition." The jaspery 

 rocks of San Francisco are worthy of description ; the green, red and 

 yellow varieties occur in the same vicinity, they form a series of layers 

 averaging two inches in thickness, and varying from half an inch to four 

 inches ; the layers are distinct and separted by open seams, and on the 

 front of bluffs or ledges the rock has a riband-like appearance, the layers 

 coalesce and sub-divide without regularity though uniformly parallel, 

 they are often twisted, and thus change at short intervals from a vertical 

 position to a dip of twenty degrees." 



The colors red and yellow are often mingled and sometimes appear as 

 parallel bands ; in some instances, the surface is red while the rock is 

 yellow beneath, this may have resulted from the burning of a tree on the 

 spot, for by heat the yellow varieties readily change to red ; a small spe 

 cimen had an agate-like structure as though formed from an aqueous 

 solution. 

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