3IO CALIFORNIA ACADEMY OF SCIENCES. 



chemical and microscopic examination, that the White 

 shale is of volcanic origin. He estimates its thickness at 

 over looo feet. 



There is, however, one feature which would seem to 

 contradict that theory. At Santa Cruz and for a short 

 distance south, the bluffs are formed of the fossiliferous 

 Transition beds. The structure is a shallow syncline. Plate 

 xxiv. Going north from the lighthouse the lower of the 

 Transition beds are crossed, as shown in the section, plate 

 xxiv, and the top of the White Miocene shale reached. 

 As the bottom of the Transition beds is approached, the 

 beds, take on more and more the character of the White 

 Miocene shale until before the parting is reached they 

 become indistinguishable from it, showing that the condi- 

 tions held over from the one period to the other. Fur- 

 ther, as mentioned below, its apparent existence in the 

 middle of the Merced series on Seven Mile Beach. 



Occurrence. — The White shale is almost wanting on the 

 northeastern slope of the mountains. A small exposure 

 occurs on the Menlo Park-Searsville road, a mile or two 

 from Searsville ; also, on the road on top of the ridge, 

 half a mile south of the Searsville-Pescadero road. But 

 on the west side of the main ridge it forms one of the 

 principal rocks. One of the best exposures in the Santa 

 Cruz Mountains is along the coast from Scott's Creek 

 south to Santa Cruz. Here it occurs dipping gently to 

 the ocean and can be well studied in the ravines which 

 have cut down through it. On the south point, at the 

 mouth of Wood's Gulch on Seven Mile Beach, two or 

 three hundred feet above the beach, there occurs an out- 

 crop of rock identical in appearance with the White 

 shale. Its presence here in the middle of the Merced 

 series is difficult to explain, but will be touched upon later. 

 Considering the thickness and extent of this formation on 



