172 REPORT OF THE AMERICAN COMMITTEE. 
Prof. Le Conte thinks the lower stratified crystalline rocks 
are mostly aqueous, raetamorphosed by heat and water. But 
recent investigations have shown that igneous rocks may take on 
schistose form by pressure and shearing. So tliat it is often 
(difficult) to distinguish between the two kinds. 
Prof. Irving says : " It is hard to answer the question as put. 
(«.) The great Archean gneiss is of wholly doubtful origin — the 
appearance being more that of an igneous origin than anything 
else — but I do not hold this, (6.) Many Archean schists, etc., 
are demonstrably altered eruptives. (c.) The true Huronian 
rocks are mainly sedimentary {e.g. quartzites, graywackes, etc.). 
(d.) Some of the Archean (pre-Huronian) rocks are very prob- 
ably volcanic fragmentals, etc." 
Dr. S. F. Emmons says: "(1.) No. (2.) I am inclined to 
regard them as of aqueo-igneous origin, that is, that they were 
not absolutely amorphous sediments like those of later forma- 
tions, and that the subsequent pressure combined with aqueous 
metamorpliism produced or intensified bedding, and caused a 
certain amount of change and re-arrangement of the mineral 
constituents." 
Mr. Walcott answers : " As far as my field observations 
have extended, the lower stratified crystalline rocks are largely 
of aqueous origin raetamorphosed by subsequent agencies. In 
some instances, large deposits are of igneous origin, inter-bedded 
and inter-stratified in the strata of sedimentary origin." 
Prof. George H. Williams replies : " I think that the 
oldest crystalline schists are in part sedimentary and in part 
eruptive, although the conditions under which both were formed 
must have been very different from what they are at present. I 
consider both classes to have been profoundly metamorphosed, 
and I think that the same metamorphosing agencies may have 
produced rocks nearly identical from such masses as were origin- 
ally very different, in case their chemical composition was much 
alike." 
Prof. C. II. Hitchcock is willing to accept Dr. Hunt's 
crenitic hypothesis long enough to answer (1,) (2) and (3.)* 
* It might be inferred from this, as (3) was intended to mean sometimes one 
and sometimes the otlier, and to be equivalent to (1) and (2), bnt actually said 
"partly one and pai-tly the other," that Prof. Hitchcock means sometimes of 
aqueo-igneous, sometimes of igneo-metamorphosed and sometimes both, but 
the reporter interprets it without the latter clause. — Reporter. 
