118 (,)UICKS1LVER DEPOSITS OF THE PACIFIC SLOPE. 



The theory of the origin of serpentine most usually entertained is that 

 it results from the alteration of other minerals. There is much variation of 

 opinion, however, as to what minerals may j'ield serpentine. Breithaupt is 

 said to have been the first to detect the pseudomorphosis of serpentine 

 after hornblende (1831) and to infer the derivative character of serpentine 

 rocks. Later, serpentine was found pseudomorphic after a long list of min- 

 erals. Olivine, brucite, hornblende, augite, diallage, chondrodite, calcite, 

 staurolite, dolomite, spinel, chromite, mica, and garnet are mentioned by 

 Prof J. Roth. Prof J. D. Dana has personally identified the greater part 

 of this list from a New York locality and also found pseudomorphs after 

 apatite.' Bischof, Professor vom Rath, and others have shown that the 

 conversion of feldspars to serpentine is probable, and, at the congi-ess of 

 Bologna, Professor Szabo, as reported by Mr. Lotti, stated this as his opin- 

 ion; but I am not aware that full proof of this change has ever been- 

 offered. That it occurs in the rocks of the Coast Ranges, however, seems 

 beyond doubt. 



In 1866 Professor Sahdberger^ and in 1867 Professor Tschermak^ studied 

 the transformation of olivine rocks to serpentine, thougli neither of them 

 asserted that olivine, which had long been known to yield serpentine, was 

 the sole source whence serpentine was derived. "The occurrence of em- 

 bedded pyrrhotite," Professor Sandberger sa}'s, "may be said to be almost 

 characteristic of the serpentines which have been derived from hornblende 

 rocks, and the same mineral occurs in serpentines which are derived fi-om 

 diabases." Professor Tschermak, though stating that the masses known as 

 serpentine and schiller-spar rocks, which he had had an opportunity of ex- 

 amining, all contained olivine as a principal constituent, also remarks that 

 diallage and bronzite grains are often converted into schiller-spar in these 

 rocks. For some time afterwards, however, there was a sti-ong tendency to 

 ascribe almost all serpentin.e to the alteration of olivine, which was found 

 to be more widely distributed and mere frequent than had previously Ijeen 

 suspected. Thus, in 1873 Professor Rosenbusch wrote: "It appears to be 



1 Am. Jour. Sci., 3d series, vol. 8, 1874, p. 380. 



■^ Neues Jahrbuch fiir Miueral., 1860, p. 385; ibid., 1867, p. 171. 



3 Ibid., 1868, p. 88. 



