Lawson. J 



Post-Pliocene Diastrophism. * 



147 



Measurements for Thickness of Merced Series in Cliff Section, from 

 Mussel Rock to Lake Merced. 



Distances on 

 shore, beginning 

 at north side of 



Mussel Rock. 



RANGE OF'STRIKE AND DIP. 



Actual thickness 

 of strata crossed 

 by line of section. 



2,239 ft. 

 1,062 " 



812 " 

 1,614 " 

 1,500 " 

 2,250 " 



625 " 



6, 2 so " 



3,646 " 



19,998 ft. 



S«V 2 OOO ft. 



Strike* 134 to 108 , Dip, 15 to 28 

 108 , " 28 to 54° 



108 to 114°, " 54 to 72 

 " ii3°toii9°, " 59° to 75 

 'i ii8°toi34°, " 75°to 5 8° 

 119 to 137 , " 58 to 72 

 137° to 1 40 , " 50 to 1 8° 

 Strike parallel to shore line, /. e., to line of section 



Strike, 150 to 166 , Dip. 39 to 5 



Total thickness of Merced series exposed 

 in section, 20.000 ft., or 3.78 miles in length 



608 

 646 

 696 

 ,302 

 989 

 ,198 

 187 

 o 

 208 



ft. 



5,834 ft. 



*The bearings refer to the true meriidan and read from 0°=N, in the direc- 

 tion in which the hands of a clock move. 



At the summit of the volume of strata here measured, there is 

 evidence of scouring of the beds by current action, and the depo- 

 sition of sandstones upon the beds so scoured in unconformable 

 relation. At this horizon also appear peaty beds. This unconformity, 

 together with the appearance of the peaty beds, is assumed by the 

 writer to mark the close of the Pliocene sedimentation, and the 

 hundred feet or more of tawny sands and sandstones which repose 

 upon these peaty beds in nearly horizontal attitudes, are therfore 

 regarded as of Pleistocene age. 



Here, then, we have marine Pliocene sediments laid down to a 

 thickness of over one mile, a condition of affairs unparalleled, so far 

 as our records show, on this continent. It is not supposed that the 

 marine Pliocene of the coast has in general a thickness equal to that 

 of the Merced series. It is undoubtedly a local or delta accumu- 

 lation at the former outlet of the drainage of the country. In this 

 respect we have its modern analogue in the broad, flat embankment 

 accumulating in front of the Golden Gate. In the great Valley of 

 California we have, however, Pliocene and Pleistocene sediments 

 (delta material, probably mostly non-marine) to a depth of at least 

 2,000 feet. There can be little question as to the propriety of cor- 



