372 The American Geologist. June, i89i 
enclosing schists. The significance of the analogy is that if the writer's 
structure of the South mountain be correct, these " quartz conglomerate 
schists" (as they are also called by him) represent the lower or nucleal 
anticlinal of the complicated series of folds representing this mountain 
chain and were considered as immediately overlying the Laurentian 
(See Reports 2d Geol. Survey of Penna. Vols, C 2, C 3, and C 4). In 
Pennsylvania, however, they were not associated with iron ores. Both 
specularite and native copper, however, are associated on the East flank 
of this mountain with chlorite schists and thin beds of the rocks named 
jasper by H. D. Rogers, and shown by Hunt to consist of a paste of or- 
thoclase mingled with extremely finely divided quartz grains. The cor- 
respondence between these phenomena in the Vermilion range in 
Minnesota and the oldest part of the Appalachian system in Pennsylva- 
nia is of great interest. 
A strong case is made for the distinction of two periods of brecciation 
of the jaspilyte. The first period being at or about the time of the pro- 
duction of the ore and jaspilyte and the second being with much show 
of reason ascribed to primordial time. 
Dr. Hensoldt's argument in favor of the precipitation origin of the 
jaspilyte deserves to be well considered, but in view of the very impor- 
tant bearing the question of genesis has on a large series of rocks in the 
East it should be passed through the probation of criticism before it is 
finally accepted. 
His plea is in short that under a moderate magnification this rock 
constituent exhibits the " mottled " appearance peculiar to novaculyte 
and hot-springs deposits. He finds in the quartz of the jaspilyte the 
same diversity in color with rotation around an axis, and the same 
absence of fluid enclosures as in the well known deposits of amorphous 
silicas. 
He finds, however, a difficulty in the comparative uniformity and more 
or less hexagonal outline of the grains. His conclusion is both 
plausible and bold. He imagines a series of volcanic irruptions under a 
hot and dense sea-water charged with free hydrochloric, sulphuric and 
other acids. The iron of the magnetite in these lav;\s was, by reason of 
its greater specific gravity, first deposited as a fine mud, and following 
this the silica was deposited in drops as gelatinous silica. These drops 
pressing upon each other effected the "hexagonal outlines" as is the 
case with basaltic columns. The salts of calcium and magnesium being 
of low specific gravity were transported elsewhere. He further supposes 
that there was usually a cessation of the deposit of the jaspilyte while 
the materials of the green schist were being thrown down, but that oc- 
casionally they were thrown down together; and that after the deposit 
of a few thin beds these were disrupted and contorted before the forma- 
tion of the next succeeding bands. His hypotheses are ingenious but 
cannot be said to be fully satisfying. 
The authors feel justified in announcing that from the widest com- 
parison of all the available data concerning the Keewatin and other ores 
" the Keewatin ores of Minnesota as produced from the mines at Tower 
