174 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



tainly not surprising. Neither of these facts even tends to prove that the 

 primeval rocks were not granitic or that they are now nowhere exposed. 

 How primeval granite is to be discriminated in all cases and with certaint)' 

 from that which was erupted in subsequent geological ages or from highly 

 metamorphosed rocks is another question, to which a definite answer cannot 

 yet be given. At present general evidence only is attainable. 



California granites. — Granite uuderlies the greater part of the State of Cali- 

 fornia. This granite must be exposed to very different depths. The Sierra 

 has been undei'going erosion ever since the early Paleozoic, and on the lower 

 portions of its eastern flanks are metamorphosed strata not younger than 

 the early Mesozoic. At the McCloud River the Carboniferous also appears 

 to rest on granite. The granite of the Coast Ranges has been covered by 

 sediments a large part of the time which has elapsed since the Paleozoic 

 and has been fnv less exposed to erosion than that of the Sierra ; yet 

 granites from the various localities are almost indistinguishable. Though 

 there may be granites within this area of different origins and ages, I can 

 see no reason to suppose that the great underlying mass is not substantially 

 one It is probably continuous with the granitic areas of Idaho and Arizona 

 and is too extensive to be regarded as an eruption or a series of eruptions. 

 Were it metamorphic, evidences of the fact would probably be frequent, 

 whereas, so far as is known, there ai-e very few localities in the State that 

 suggest this derivation. While both metamorphic and eruptive granites will 

 probably be found, the main mass must be at least as old as the Archrean, 

 and, while I do not assert positively that it is primitive granite, this appears 

 to me far more probable than any other hypothesis. As was pointed out 

 above, the formation of more or less gneissoid rock probably accompanied 

 that of the primeval granite and the presence of such material in a granitic 

 area does not prove that it is not primeval.^ 



California lavas. — Tlio Uivas liave unquestiouably come xip through the 

 granite and are of infragranitic origin. There is no direct evidence wliat- 



'A portion of tlie primeval crystalline rooks, though perhaps a small one, was probably plagio- 

 clastic. It wonld be difficult otherwise to account for the qiiautity of soda in the clastic rocks. If 

 Professor Lagorio is correct, as ho sosms to mo to be, in asserting that sodium silicates separate from 

 magmas more readily than potassium compounds, it would seem that oithoolase should have predom- 

 inated in the outer crust of the earth, or iu the primeval granitic rocks, and that plagioclase should 

 have predominated in the infragranitic rocks, or in the lavas. This, of course, accords with observation. 



