26 CALIFOENIA ACADEMY OF SCIENCES. 



The fauna of Crawfish George's consists of one hundred and fifty-three 

 species, of which forty-eight are pelecypods, one hundred are gastropods, three are 

 scaphoiwds, one is an echinoderm, and one is a crustacean. It is similar to the 

 upper fauna of the San Pedro bluflf, with the exception that it affords a few species 

 common in the lower San Pedro series that are not found in the upper beds at any 

 other locality. Another noticeable fact is the great preponderance in numbers of 

 gastropods over pelecypods. The fauna seems to be that of a rocky beach. 



All along the cliff, from Crawfish George's to Timm's Point, the gravel lies 

 unconformably in disconnected masses on the Miocene shale, and is covered by soil 

 varying in depth from three to ten feet. From Timm's Point to the north along the 

 bluff this formation is not exposed until a point is reached a little north of the rail- 

 way cut. Here the typical gravel of the upper San Pedro series rests unconformably 

 upon the lower San Pedro gray sand, and is overlain by a layer of soil. The 

 upper San Pedro gravel (see diagram D, Plate XXII) again outcrops in the bluff 

 north of the San Pedro Valley, but is covered in this bluff by a sandy stratum 

 between it and the soil. This gravel stratum runs along the bluff near the surface 

 until it reaches a point about two hundred yards north of the valley, where it 

 suddenly dips at an angle of 45° for eight feet, resting all the while on the eroded 

 surface of the lower San Pedro strata. Again changing its dip to normal, it disap- 

 pears under the detritus at the mouth of a short ravine. The unconformable position 

 of the upper gravel on the lower gray sand is very apparent a few yards south of 

 the ravine, where fragments of the lower San Pedro strata are found in the upper 

 gravel. After the deposition of the lower San Pedro beds there came a period of 

 uplift, during which they were eroded; then came a period of depression, during 

 which the upper San Pedro beds were deposited on the eroded surface of the 

 lower series. 



A heterogeneous series of strata, composed of alternating beds of sand and 

 gravel, occurs above the gravel stratum at the ravine and to the north of it. 

 These overlying beds dip gently to the north, but the series does not decrease 

 in thickness to the north for the reason that other strata begin near the top of 

 the bluff, and thus make a nearly horizontal surface to the top of the series, which 

 is overlain by soil to the thickness of from two to ten feet. The lower strata 

 along this bluff are of fine sand, fossiliferous in places. Near the top of the 

 bluff, however, the strata are composed of coarse material, a distinct layer of gravel 

 cemented with lime and containing many well preserved fossils forming the top layer. 

 This top stratum first appears at the top of the bluff about one hundred feet south of 

 the ravine. From this point south of the ravine it can be traced north along the 

 bluff near the top, around the north end of the bluff, and back again on the west side 

 of this promontory for several hundred feet. About six feet below the top gravel 

 stratum is another layer rich in fo.ssils. The beds below these last two are sand and 

 gravel deposits of varying composition, nearly all, however, fossiliferous. Some of 

 these lower strata show sand-dune bedding, while others are horizontal. This alter- 

 nation of bedding would indicate a period of alternating conditions of elevation and 



