Anderson.] 



Point Reyes Peninsula. 



123 



underlain by Miocene sediments. No more granite is seen along 

 the shore from this point southward, but along the bay they are 

 only imperfectly covered. Along this side of the peninsula the 

 granite comes to the surface and is more or less continuous with the 

 second area of granite further south. 



This second area, which forms the largest body of granite on 

 the peninsula, lies west of the head of Tomales Bay. It embraces 

 Vision Hill, and a, large portion of Whittenberg Hill, with almost 

 the whole of the ridge connecting them. From near the entrance 

 of Bear Valley, the eastern margin of the granite follows the 

 county road toward, and along the shore of the bay to the point, at 

 which the road turns westward through the hills. Here it is 

 interrupted, for a few hundred yards only, by an exposure of thin- 

 bedded siliceous schist, which rests upon the granite at the water's 

 edge. Northward, beyond this point, the granite is exposed along 

 the shore for several miles. Along the western flanks of the ridge 

 which follows the shore of the bay the Miocene sediments overlie 

 the granite, and make its western boundary much less regular. 

 The area widens gradually, however, from the north, where it is less 

 than a mile in width, until at a point opposite the head of Tomales 

 Bay, its greatest width is a little more than three miles. Scattered 

 patches of sedimentary rocks cover the northern portion of this 

 area. A tongue of these sediments occupies the depression to the 

 north of Vision Hill, while the bold spurs of the hill farther to the 

 south extend the granite westward into the border of the Miocene 

 rocks. The most southern exposure of granite belonging to this 

 area that was observed, was on the eastern brow of Whittenberg 

 Hill, opposite the hamlet Olema. 



The third area of granite is distinct and entirely separated from 

 the preceding two, at least superficially, by the sedimentary rocks 

 of the Miocene in the lowlands surrounding Drake's Estero. This 

 area of granite is at the extreme southwestern promontory of the 

 peninsula. It is smaller than either of the other two areas, and 

 forms only a narrow ridge extending in an east and west direction 

 for about a mile and one-half. It has a general elevation of about 

 five or six hundred feet, though at its eastern end it drops some- 

 what lower than this. The southern face of this ridge is a precip- 



