PREFACE. XV 



to which was afterwards added a valuable suite of specimens 

 from the Humboldt eastern range, made by Mr. Homfray, 

 have been elaborated by Mr. Gabb, in Section II. 



In the autumn of 1863, Mr. Gabb was engaged by me to 

 conduct some explorations outside of California and the regu- 

 lar work of the Survey. He made a trip, of three months' 

 duration, through Oregon and Washington Territory to Van- 

 couver Island, and collected a considerable number of Ter- 

 tiary and Cretaceous fossils, making important additions to 

 the little previously known of the geology of that extensive 

 region. He has now joined an exploring party through South- 

 eastern Oregon, emphatically a geological terra incognita, 

 from which region he can hardly fail to bring back facts of 

 importance. The expedition started from Fort Klamath, at 

 the north end of Klamath Lake, about the 20th of June. 



During the spring of the current year Mr. Clarence R. King 

 made some valuable explorations in the Humboldt ranges of 

 Nevada Territory ; he also, previously to that, had made an 

 interesting contribution to the geology of the Sierra Ne- 

 vada, by the discovery of Belemnites in close contact with 

 one of the great auriferous quartz veins of the central gold 

 mining region (on the Mariposa estate), thus adding a very 

 important link to the chain of evidence going to show that the 

 auriferous slates and metamorphic rocks of California are, to 

 a large extent at least, of Secondary age, and not Palaeozoic, 

 as had heretofore always been assumed, without evidence. 

 Messrs. Brewer, King and Hoffman are now, or have been 

 up to a quite recent period, engaged in the high Sierra, 

 around the head-waters of King's River, and the other 



