p. 3

4

After determining, by the more minute and detailed exam-
inations, the stratified nature of these rocks, we are able to
discover in the larger masses, and the hill escarpments the
direction and dip of the strata, which are extremely obscure,
and rendered more difficult of observation by the numerous
joints. Besides these determinations, I have in two or three
localities been able to trace these quartzites upward till the
beds become conglomeritic; the pebbles consisting of the
crystalline quartz, (usually of a brown color,) which vary from
the size of peas to a foot or more in diameter. The darker
materials gradually become mixed with a lighter colored sand,
and sometimes a notable proportion of argillaccous matter;
the mass loses its metamorphic aspect, and we find ourselves
almost imperceptibly investigation the base of the Potsdam
sandstone.

It must not be understood, however, that there is any pass-
age from the one to the other that would indicate a synchron-
ism of the two formations. On the other hand, the quartzite
had been deposited as a coarse and find sand, (with sometimes
pebbles, had become metamorphosed and the mass raised in
low axes before the commencement of the Potsdam era. The
breaking up of this mass gave the pebbles of quartz, etc.,
which lie at the base of the Potsdam sandstone; and these
pebbles,) with an accumulation of sand from the breaking up
of the mass continue the color and aspect of the rock below,
till the influx of lighter colored sand changes the character
and color of the whole.

I regard this discovery of the nature of these underlying
masses to be a matter of considerable interest; and since the
areas occupied by such rocks are limited, and it is nearlly im-
possible to trace a connection between any two of them, it
becomes important to collect material from numerous localities,
for the purpose of comparison with the more extended areas
of older metamorphic rocks.

These metamorphic masses are, in all probability, extensions
of the Huronian formations of Canada; and though not fa-
miliar with the latter in its typical localities, I am inclined to
refer them to that period, since they do not correspond with
the Laurentian rocks known to me through investigations in
northern New York.

I have considered these facts of sufficient interest to the
science of Geology and to the survey to communicate them in
the present report. I shall continue this investigation, and
hope to be able hereafter to show the relations of all these
metamorphic masses to formations of known geological age.