330 [April; 



thickness, and this is believed to be much less than it in reality is. The under- 

 lying strata, which are similar in their appearance, are probably equally fossili- 

 ferous, but this has not been demonstrated by examination. Their thicknesses 

 were respectively, 1, 12, 2 and 10 feet, which, added to the thickness of the 

 upper stratum, make a total of seventy-five feet. This is exclusive of the com- 

 pact siliceous strata, which are presumed to be also fossiliferous. These siliceous 

 layers are very extraordinary, some of them being like semi-opal in density, and 

 in the character of their fracture, the surfaces being curved and vitreous, and 

 the edges sometimes as sharp as glass. Their color varies from white to drab, 

 or fawn-color, and is sometimes pink ; some specimens resemble ivory or horn 

 in color and translucency. Silica appears to be the constituent, and it must have 

 been deposited in an impalpable form. The mineral characters of some of these 

 strata are like those of specimens of surf-worn boulders that I picked up on 

 the beach at San Pedro. These consist of silica charged with bitumen, and when 

 broken present a conchoidal fracture and a resinous appearance. It is expected 

 that these siliceous specimens will not only be interesting chemical^, but that 

 they will furnish beautiful objects for the microscope. 



On the top of this formation there is a rudely stratified or assorted mass of 

 boulders and gravel, like the accumulation along a beach. It is, in fact, a layer 

 of beach-shingle, and it includes, among pebbles of granite and other rocks, 

 water- worn masses of the compact siliceous rock, probably derived from the sub- 

 jacent beds. One of these siliceous masses that was dark colored and probably 

 bituminous, was found to be perforated by boring testacea. This was an unex- 

 pected and interesting discovery; for, here were masses of rocks of tertiary age 

 that had been exposed and perforated by marine shells before being broken off, 

 rounded and worn by the surf among other and harder rocks, and thrown on a 

 beach by the retiring waters. The beach still remains, and rests exposed on the 

 very summit of the hill, covering the edges of the strata a remnant of a for- 

 mer shore now five hundred feet above the ocean. 



This interesting formation, teeming with the skeletons of microscopic organ- 

 isms appears to overlie and to be conformable with the tertiary strata that 

 underlie a part of the town of Monterey and extend to and beyond the Mission 

 of San Carlos. These strata rest upon a porphyritic granite, which forms 

 the projection of the coast called Point Pinos, and is the bulwark of the bay. 



Several quarries have been opened in the sedimentary formation near the 

 town, and it is seen to consist of regular strata of light-colored argillaceous and 

 arenaceous material ; the particles being very fine and firmly impacted, so that, 

 in some places, the strata break with smooth, curved surfaces, and have a semi- 

 vitreous lustre. A large quantity oi stone has been removed from these quar- 

 ries and used in the construction of the buildings and walls of the town. The 

 large Court House built by Walter Colton, and the church erected in 1794, are 

 constructed of this stone, and the sharp edges and angles which are retained by 

 the blocks in the walls of the latter show that the material has great durability 

 and resists decomposition exceedingly well. 



When the blocks are freshly broken out from the quarry they are easily hewn 

 into shape by an axe ; being extremely light and free from coarse sand or 

 gravel. They harden slightly on exposure, but may be cut away with a knife. 

 The color is a light buff or yellow, of various shades, passing into fawn color 

 and drab ; some of the beds are quite dark, being greenish black, or a dark olive 

 brown. The prevailing color is, however, a light drab or yellow, very similar 

 to the color of bath brick or lithographic stone. It is not unlike the former in 

 density, being porous, and, when dry, ic absorbs water with rapidity ; in this 

 respect and in density, it also resembles biscuit-ware, or the material of the 

 porous cells of Grove's batteries. 



These strata are fossiliferous, and many of the compact layers when split up 

 into slabs parallel with the fine lines of stratification are found to be covered 

 with impressions of small bivalve shells, lying thickly together, sometimes one 

 within the other, as if they had fallen upon the bottom of a quiet sea. The 

 most abundant shell is a small Td-lina, which Mr. T. A. Conrad has described 

 for me and named T. coi/gesta. It is also found in similar strata at San Carlos, 



