character of the minerals and ores which occur in each formation or 

 group of strata having been first determined, the details of their mode 

 of occurrence, their relative abundance, and the facilities which may 

 exist in each separate district for making them economically available, 

 must, after the preliminary general work has been done, be the object 

 of more special and detailed examinations. It is not, however, the busi 

 ness of a geological surveying corps to act to any considerable extent 

 as a prospecting party; to do this would require that we should confine 

 our operations to a very limited area. The labor of the whole corps for 

 an entire season would not suffice to throughly prospect mare than a 

 few hundred square miles in a very rich mineral region, and we should 

 often have to engage in expensive mining operations to decide what 

 was really of permanent' value. It is our task, rather, to limit the field 

 of research, and to show to others where their labor will be best 

 bestowed, preventing foolish expenditure of time and money in searching 

 for what our general geological investigations have determir.ed not to 

 exist in sufficient quantity in certain formations to be worth working. 

 Especially in the first years of our work in a State of such immense 

 area as California, our labors must have more the character of a geo 

 logical reconnoissance than of a detailed survey. 



In the department of palaeontology one volume has already been pub 

 lished. This contains, in the first section, a description of the carbonif 

 erous fossils of Bass' Banch, the only locality where any well preserved 

 organic remains of that age have been found within the State. The 

 second section is devoted to the fossils of the triassic rocks, including 

 all which have thus far been discovered in California and on its borders. 

 While we have abundant evidence that a formation equivalent in geolo 

 gical age to the Alpine trias, or the beds of Hallstadt and St. Cassian, 

 occurs over a vast area, and forms an important part of the metalliferous 

 belt of the Pacific coast, and probably on both sides of the Sierra, and 

 while fossils of this age have been found at several localities within the 

 borders of California, our most ample supply of well preserved specimens 

 has come from the Humboldt mining district in Nevada. Hence we have 

 included in our descriptions of the triassic fossils those of that region, 

 although some among them have not yet been found in California. 



The third section of the volume of palaeontology is devoted to the 

 Jurassic fossils of the Sierra Nevada; or, rather, to such as had been dis 

 covered at the time of its publication. These fossils are all from the 

 localities near Genessee Yalley, noticed in section eleven, Chapter IX of 

 Yolume I, of the Geology. At the end of that volume a few pages 

 will be found containing descriptions of the Jurassic fossils of the aurif 

 erous slates in Mariposa County, from the localities discovered by Mr. 

 King, and in close proximity to one of the great quartz veins of the 

 mining region proper. This paper, by Mr. Meek, and which is illus 

 trated by a steel plate, was published in the geological volume to pre 

 vent delay, as the question of the geological age of the auriferous slates 

 is one of great interest, and some time will necessarily elapse before the 

 second volume of the palaeontology will be ready for publication. In 

 the meantime, and during the past year, Mr. Eemond has traced the 

 belt of fossiliferous Jurassic rocks from the Merced River to the Stanis 

 laus, finding several genera and species different from those previously 

 obtained from this formation. These, together with such other fossils of 

 this age as may hereafter be discovered in the State, will be described 



d published in the second volume of the palaeontology. 



The fourth section of the volume in question is devoted to the creta- 



