XVI PREFACE. 



streams between that and the Merced, — a region from which 

 we can hardly expect any considerable additions to our 

 palaeontological materials, while, on the other hand, their 

 geographical discoveries, and their additions to our know- 

 ledge of the topography of the State, have been of great 

 importance. 



Mr. Remond, having been for some time detached from 

 the Survey, has resided in Sonora, Mexico, and has made 

 numerous geological observations, an abstract of which will 

 be communicated in the forthcoming volume of this Report 

 especially devoted to Geology. 



The observations of the Survey, taken in connection with 

 those already and hereafter to be made on the north, south, 

 and east of California, will enable us to form a general idea 

 of the geological structure of a vast area of country border- 

 ing on our Pacific coast, and we trust that we shall be able, 

 in due time, to furnish a geological map of a large portion of 

 the western side of our continent; a map which, it may 

 with truth be added, will have little resemblance to those 

 heretofore published. Such a map, however, will of course 

 only present an outline of the geology of this region ; for 

 anything like a thorough exhibition of its structure we shall 

 have to wait many years, since it is a field sufficiently ex- 

 tensive, and difficult of exploration, to require an almost 

 unlimited amount of labor before its details shall have been 

 fully wrought out. 



It will be proper, in this connection, to mention, in as 

 concise a manner as possible, some of the principal results 

 of our Survey, and particularly those which relate to the 



