Vol. XI] D1CKERSON—PT. REYES AND SANTA ROSA QUADRANGLES 555 



in turn are overlain by basalt. Plate XXXVIII shows the 

 approximate sequence in Lynch Creek. The cavities in the 

 overlying basalt are in some places filled with a thick petroleum 

 residue and some of the dark brown, medium-grained sand- 

 stones are impregnated with petroleum. These sands yield a 

 very good petroleum test when shaken out with chloroform. 

 The Petaluma formation is not a probable source of the oil but 

 it apparently has come up from below, along a fault. The 

 Monterey shale is probably its original source and this group 

 apparently underlies the Petaluma formation in the region. 

 Another indication of petroleum, a seep, is reported about one 

 mile southwest of Ducker's ranch house. Two wells of 100 

 feet and 400 feet in depth were drilled on the Ducker ranch. 

 A heavy gas pressure was reported. 



SONOMA PETRIFIED FOREST 



It is always a difficult question to decide the relative im- 

 portance of unconformities and the time intervals between 

 successive outbursts of lava, volcanic ash, or tuff-breccia. A 

 very rough measure of time is found at the Sonoma Petrified 

 Forest, which is located about eleven miles northwest of 

 Santa Rosa and five miles west of Calistoga, a town at the 

 head of Napa Valley. Most of the trees in this "forest" were 

 covered, or nearly covered, by tuff and tuff-breccia, belonging 

 to the Sonoma group of volcanics, when discovered by Mr. 

 Chas. Evans in 1871. Mr. Evans excavated the trees and 

 exposed several large redwoods and firs to view. This ex- 

 cellent work has been continued by the present owners, Mr. 

 and Mrs. D. G. Bockee, and there are now about eight fine 

 trees which have been laid bare for inspection. (See Figures 

 1 and 2, Plate XXXI.) The "Queen of the Forest" is a 

 large redwood about twelve feet in diameter at its base. 

 About eighty feet of this tree is preserved in stone. As the 

 picture indicates, it is broken somewhat, but its fragments 

 were so arranged when it was excavated that the position of 

 the tree as it was toppled over and buried by a great flow of 

 volcanic mud and ash, has been maintained to this day. A 

 smaller but more nearly perfect specimen is shown in Figure 

 2, Plate XXXI. This tree was almost completely buried in 

 tuff-breccia when discovered. Its natural taper is readily 

 apparent and like the "Queen of the Forest" its top is toward 



