CONCLUSIONS 445 



correct, we are forced to conclude that the original from which the 

 serpentine was derived must have been some member of the gabbro 

 family. The alumina, therefore, could be derived from the presence of 

 an aluminous pyroxene, or more probably from the feldspar. The 

 calcium could likewise be derived from the same sources. The thin 

 sections suggest that a very large part of the calcium is now present as 

 carbonate. It is not, however, universally present in all sections. 



Conclusions 



It is believed that the petrographical facts, as obtained from the thin 

 sections of the serpentine-amphibolite contact on the Tucker property, 

 are sufficiently evident to render the application of Professor Emerson's 

 explanation of similar deposits impossible. It must be admitted that a 

 number of the thin-sections from the serpentine area show an apprecia- 

 ble amount of calcite. But an excess of calcium carbonate is by no 

 means a proof of a derivation from a limestone. It is quite as easily 

 accounted for as a secondary product from pyroxenic contents of an 

 eruptive or igneous mass. 



It is also significant in this connection to note that petrographic and 

 chemical investigations of serpentine deposits, both in the United States 

 and other countries, have almost invariably proven that such rocks are 

 derived from some member of the basic igneous series. The accompany- 

 ing tabulation of explicit statements, culled from the literature, contains 

 but two cases of a derivation from a pyroxenic limestone out of a total 

 number of twenty-six occurrences. While this statement contains noth- 

 ing of the nature of proof with reference to the area under consideration, 

 it nevertheless reveals the significant fact that the conclusions reached 

 with reference to the Belvidere serpentine are quite in accordance with 

 the predominant views held by the vast majority of petrographers. 



Concerning the origin of the amphibolites, I can only say that so far 

 as lithological relationships in the field and petrographical characters 

 are known no data have been found which even offers a suggestion as to 

 the nature of the original rock from which the amphibolite was derived. 

 It is not, however, associated with any argillaceous limestone, such as 

 has been recognized by Professor Emerson, in the Old Hampshire county 

 occurrences. 



Locality. Analysis derived from. 



Colfax folio, California Peridotite. 



Downieville folio, California . . . Peridotite, pyroxenite. 



Jackson folio, California Peridotite, gabbro, pyroxenite. 



Mother Lode folio, California. . Intrusive, original not determinable. 

 Placerville folio, California Peridotite, pyroxenite. 



