MARYLAND GEOLOGICAL SURVEY 201

the other toward Labrador. Upon this great skeleton the continental
area has since been gradually built up by accumulation of sediments
along its borders; yet in these early days there were additional areas
above the seas which furnished the source of some of this sedimentary
material, but which have themselves more or less completely disap-
peared. We must to-day draw our inferences regarding the character
and extent of these areas both from the nature of the rock comprising
their scanty fragments and from the character and relations of the
strata of later date. There is no positive evidence that we have rep-
resented in Maryland any of the rocks of this earliest portion of
Archean time, although it is not impossible that part of the gneiss
complex may represent it.

There is much evidence in support of the view that the later por-
tion of Archean time, which has been referred to as the Algonkian
period, is represented by rocks of many varieties within the limits of
the state of Maryland. The proof of this is seen not only in the
character of the rocks themselves, but also when we consider the vast
thickness of sediments which accumulated later, during the whole
lapse of Paleozoic time, in the great trough in which the Appalachian
mountains were formed. We are compelled to assume a great con-
tinent or mountainous mass lying along the southeastern edge of our
present continent and extending perhaps eastward well into, if not be-
yond, the limits of the Coastal Plain, although we can form but little
conception of the form and area of this ancient land mass. That it
must often have stood at some considerable elevation above sea-level
and have borne streams of no mean proportion is shown by the rapidity
with which sediments, often coarse in nature, were furnished to the
inland sea which stretched along its western margin. To-day we have
preserved to us in the crystalline plateau which extends from New
York to Alabama along the eastern base of the present Appalachian
mountains, with a width of 300 miles in the Carolinas, the merest
remnant of this ancient continent. These rocks with the eruptives
which have broken through them are confined in Maryland mainly
to the eastern portion of the Plateau country, although on account of
structural disturbances which have taken place in the area farther