LAWbUN.] 



Geology of Carmelo Bay 



l 9 



detritus. There are, however, occasional larger bowlders, and locally, 

 as to the west of Sunium Point, these are very abundant. The 

 pebbles consist chiefly of purple and red quartz-porphyry, green- 

 stone, granite (Santa Lucia) quartz, and highly siliceous meta- 

 morphic rocks. The conglomerate is usually hard and compact, 

 and is remarkable for the shattered and cracked appearance of the 

 pebbles. This cracking is, of course, secondary and subsequent to 

 their deposition in the formation. In some cases, as on the shore 

 to the east of Carmelo Cove, the pebbles are not only cracked, but 

 are distinctly sheared or faulted along numerous fine, irregular fault 

 planes. The faulting cannot usually be detected in the matrix, but 

 can be followed from pebble to pebble, the dislocation in each not 

 exceeding one or two millimeters as a rule. These shear planes do 

 not vary greatly from the vertical. 



Occurrence. — The rocks of the series occur in three distinct 

 areas within the limits of our field. The largest of these is on Car- 

 melo Point, where they occupy, as represented on the map, a small 

 synclinal basin let down by faulting into the granite upon which 

 they rest. The attitude of the beds varies from vertical to nearly 

 horizontal, and the general structure of the basin is that of a com- 

 plex syncline, the rocks in a general way dipping from the rim 

 towards the center. Usually the strike and dip vary so rapidly 

 that it is not an easy matter to find a section suitable for a measure- 

 ment of the thickness of the series. On the south side of the ex- 

 tremity of Carmelo Point, however, the strike is fairly constant for 

 several hundred yards, and the dip varies from 20 to 26°, so that 

 a favorable section is afforded upon which to measure the thickness. 

 The estimate arrived at was 800 feet for the minimum thickness of 

 the series. 



As has already been stated, the relation of the Carmelo series 

 to the Santa Lucia granite is that of a sedimentary deposit reposing 

 upon a worn and uneven surface. The superposition is well seen 

 on the south side of the Carmelo Point, and is represented in Plate 

 2, Fig. 2, and in Plate 3. 



In so shallow a basin of such limited extent, with sandstones 

 resting on a great mass of granite in undulating folds, or in vertical 

 attitudes, it becomes a matter of much interest to ascertain how the 



