334 The American Geologist, May, 1896 
parting is reached they become indistinguishable from it, showing that 
the conditions held over from one period to the other." It would be 
interesting to know in such a case just how the parting was determined 
and what was its character. 
As concerns the base of the Merced series at Mussel Rock, and the 
possible existence of a fault there, it is sufficient to state that tlie obser- 
vations recorded in the present paper and those previously published by 
Prof. Lawson are diametrically opposed, and that the earlier interpreta- 
tion must be recognized as valid until more seriously attacked. 
Throughout the paper Mr. Ashley lays great stress upon the frequency 
and importance of the faulting that the region has undergone. While 
willingly admitting a certain amount of conspicuous, and structurally 
very important, faulting, yet one is inclined to be somewhat sceptical 
over a super abundance of convenient faults, and to prefer a suspension 
of judgment until they are brought out by detailed geological mapping. 
Passing without criticism over the purely paleontological discussion 
at the end of the paper, and, as regards oscillations during the Quater- 
nary, merely stopping to note that the two summaries of these move- 
ments given, are not strictly accordant, we revert to a subject that is 
frequently suggested by this paper, but which is, in addition, intimately 
connected with the greater part of the literature on California geology, 
■ — the misuse of the term metamorphic. This adjective, belonging to the 
petrographic side of geology, is properly applied to rocks whose consti- 
tuents have wholly or in part undergone molecular re-arrangement, and 
have crystallized into new minerals, as in the crystalline schists, or to 
those which, consisting of a single chemical compound, have been ren- 
dered crystalline throughout, as in marble. Quoting from Geikie,* 
" metamorphism is a crystalline (usually also a chemical) re-arrange- 
ment of the constituent materials of a rock. ... A metamorphosed rock 
is one which has suffered such a mineralogical re-arrangement of its 
substance." According to Dana| metamorphism is "a change in tex- 
ture, crystalline structure, or mineral constitution." The word " tex- 
ture " is somewhat ambiguous here, but is made clear by the context. 
It was to be expected that the earlier geologists, before the introduc- 
tion of modern petrographic methods, should have very frequently 
misapplied the word, as indeed they did — more particularly Whitney. 
It was less excusable that Becker should have not only continued !but 
extended the misconception. But it is difficult to find a corresponding 
excuse for the reckless way in which rocks, particularly sedimentary 
rocks, are branded as metamorphic at the present day. Beyond certain 
local contact schists, which the writer before us does not mention at all, 
(and the Gavilan limestone, which should be excluded) the group of 
rocks which he has called the "Metamorphics " has not been shown to 
contain a single rock to which that adjective is certainly and properly 
applicable, as can be seen at a glance by referring to Prof. Lawson's 
description of the Franciscan series. It is possible that the serpentine 
*Text Book of Geology, 3rd ed., p. :J19. 
fManual of Geology, tth ed., i>. 3TJ9. 
