194 EDSON S. BASTIN 
analyses of a large number of sedimentary slates and schists with 
a much larger number of analyses of igneous rocks. Such a sta- 
tistical study, the assembling of analyses which were selected 
judiciously but impartially, offered, he believed, a viewpoint from 
which the rule could be perceived in the midst of the numerous 
exceptions which special conditions introduce. ‘The result of this 
study was to confirm in general the beliefs of the geologists who 
had earlier considered this problem. In addition conclusions were 
reached as to the relative critical value of various chemical relation- 
ships. 
J. D. Trueman in a recent number of this Journal* summa- 
rized in a very useful manner the various criteria that had been 
applied for determining the origin of schists. In the section 
devoted to chemical criteria he recognized that these may be of 
service in some instances, but he seemed in general inclined to 
attribute small importance to them. 
As Mr. Trueman was good enough to refer to my article on 
this subject, I wish here to consider some of the objections which 
he raised and to elucidate further certain of the arguments that 
were brought forward in the original paper. Mr. Trueman’s 
untimely death last summer while engaged in geologic field work 
must be a source of deep regret to those who are familiar with 
his work and I take this opportunity to express my appreciation 
of the high value of the contribution he has made to the literature 
on metamorphism. Agreeing with most of his conclusions, if 
I take exception to a few of them it is in the belief that no true 
scientist regards his results as final but is eminently satisfied if 
his work stimulates others and contributes somewhat to the progress 
toward a more complete knowledge of Nature’s laws. 
The principal criteria which have been appealed to in support 
of sedimentary origin of a fresh crystalline schist are: (1) dominance 
of magnesia over lime, (2) dominance of potash over soda, (3) the 
presence of alumina in large excess over the 1:1 ratio necessary to 
satisfy the alkalies present. It should be particularly emphasized 
that the amount of the excess of potash, magnesia, or alumina is 
of great importance, a magnesia-lime ratio of 4:1 being immensely 
t Jour. Geol., XX, No. 4, pp. 300-311. 
