

INTKODUCTORY NOTE. 



Under the title of " Litbological Studies," a work is here presented to tlie public 

 which is, in pohit of fact, a continuation of the publications of the Geological Survey of 

 California, begun under my direction, in 1860. Had that Survey been completed, the 

 investigation of the rocks of the State would naturally have been one of tiie matters to 

 whicli our attention would, at the proper time, have been turned; and, after the stoppage 

 of the Survey, in planning for the elaboration of the materials in my hands, I, in 1S77, 

 determined that the litbological collections which I had accumulated, and which repre- 

 sented a wide area, should be described and classified. For this purpose Dr. "NVadsworth 

 was selected; and, a portion of his results being now ready, it is thought best that it should 

 be published, without waiting for the completion of the entire work. It will undoubt- 

 edly seem to the reader that what is here furnished does not exactly correspond with 

 or carry out the idea suggested on the title-page, namely, that this is a description and 

 classification of the rocks of the Cordilleras. The reason is this : Dr. Wadsworth having 

 been led by his investigations to place his work on a considerably different basis from 

 that built upon by other lithologists, has found it desirable, and indeed necessary, to 

 incorporate in it results obtained from the study of material not furnished by the Cor- 

 dilleran collections. In the portion of the work herewith offered to the public, rocks more 

 basic than the basalts are brought under consideration ; and in doing this, it has been 

 found that it was not possible to arrive at the end sought to be gained without using the 

 materials furnished by other regions ana by other lithologists. ShouLl this investigation 

 be continued and completed — as it is hoped will be the case, a large amount of work 

 having been already done with that end in view — the Cordilleran collections will yield 

 the chief portion of the material drawn upon for the remaining portion of the volume, so 

 that it will be found that the work is essentially based on the collections made on the 

 western side of the North American continent, the study of which gave rise to the ideas 



presented in this first part. 



J. D. WillTNEV. 



Cambridge, Mass., October 18, 1884. 



