1888.] 45 
by three hundred feet in width, and averaging about three feet in thick- 
ness, lying almost horizontal in the soil. At present somewhat more than 
two square acres of it are exposed to view in an almost continuous 
stratum. It rests here in a marshy meadow, surrounded by a mixed 
clayey sand, apparently upon the old flood-bed of the Patuxent river. At 
this point it is composed of bright, mostly compact silex, of great hard- 
ness, but with inconspicuous enclosures of kaolinic material, and closely 
resembles the common type of Potsdam sandstone. More than an acre of 
its former mass has been carried away to form abutments on the Balti- 
more and Potomac railroad. 
Here it is more substantial than in the vicinity of the Severn, and seems 
to suffer but little loss from superficial disintegration. Much of its con- 
tinuation towards the river has suffered from erosive agencies, and lies, in 
detached pieces, scattered through the woods. But in that part of the 
area, it is less densely compacted, and presents the appearance of a coarse- 
grained sandstone. 
Beyond this point, in the direction of the Potomac river, no large expo- 
sures of the white rock appear, the Cretaceous sands and clays cover the 
formation, and it is only in a few of the deepest ravines that we meet 
with the coarse ferruginous saud-rock which belongs to a higher level in 
the series. 
It yet remains to be seen whether this series of rocky strata is continu- 
ous with that which skirts the west shore of the Potomac from Mount 
Vernon southward to Acquia creek. Such examples of the stone as I 
have compared. with the varieties from Maryland are of a different kind of 
texture. And, although there are various types of structure ranging all 
the way from a coarse conglomerate to a perfectly homogeneous quartzite, 
within our territory, those from Virginia are either composed of more 
crystalline separate grains, or are more decidedly mixed with drifts of 
coarse kaolinic matter. 
On the Severn river we find excellent sections, giving nearly all the 
members of the series of strata composing the Albirupean formation. 
Directly on the river, it occupies a tract of country three and a-half miles 
wide ; but it extends in thin deposits, at intervals between the hills on the 
northwest, back through a distance of at least ten miles more, thus giving 
it, in the widest part, a breadth of thirteen and a-half miles. The more 
rocky portions of this belt occupy now, however, a width of about three 
miles, and are far from being continuously connected, either along or across 
their line.of strike. But they have not been always so re:tricted, for in 
nearly every part of the great sand area, decomposing pieces of the stone 
with the fresh sand derived therefrom may be found after a short exami- 
nation of the surface. 
On the eastern shore of Maryland, in Cecil county, the white san dstone 
appears on the surface in the form of huge boulders, six to ten or more 
feet in length, and from two to four feet in thickness. Considerable num- 
bers of these large masses project above the surface at intervals on all the 
