356 F. L. Ransome—Lava Flows of California. 



fusion with the ordinary clastic andesites abundant in the 

 same field. 



The laboratory work embodied in the preparation of the fol- 

 lowing pages was carried on in the petrographical laboratory of 

 Harvard University, and my thanks are due to Prof essor Wolff 

 for the excellent facilities "there enjoyed. I am also indebted 

 to Mr. Turner, not only for the original permission to under- 

 take the work, but for generously aiding it in many ways. 



Fig. 1. Index-map showing position of area embraced in Sketch-map, fig. 2. 



Physiography of the region. — The accompanying map on 

 page 357 embraces a rectangular strip of country 63 miles in 

 length and 14'5 miles in width, with its longer dimension lying 

 very nearly northeast and southwest. It includes portions of 

 the Oakdale, Sonora, Jackson, Big Trees, Dardanelles, and 

 Pyramid Peak atlas sheets. Considerably more than half the 

 area, however, lies within the Big Trees sheet. The extreme 

 southwestern portion, lying west of longitude 120° 30' and 

 south of latitude 38°, is taken from the northeast corner of the 

 unfinished Oakdale sheet. The topography is here only partly 



