Uhler. ] 52 [Jan. 6, 
reaches a thickness of at least twelve feet. The drift in this stratum is 
chiefly gravel, with small rounded pieces of the compact quartz, and the 
pebbles usually enter into the composition of the upper part of the brown 
sand-rock, making it more or less of a pudding stone. 
As the point near Round Bay is approached where this formation passes 
beneath the greensand Cretaceous, the brown sand-rock divides into two 
members, the upper one of which is only about a foot in thickness, while 
the lower one has a thickness of more than five feet. No large angular 
blocks were found in this part of the formation ; but on Valentine’s creek 
it is closely packed with round quartz boulders, such as are made in pot- 
holes, or in glacial rapids. 
Near the top of the greensand Cretaceous a slender drift of small quartz 
boulders and pebbles occurs, and over this rests a sinuous, flaky crust of 
finer, powdery ferruginous sandstone, the oblong chambers of which are 
closely packed with micaceous grayish sand full of glauconite. 
The Baltimorean formation seems to have been produced in a region 
adjoining the sea where accumulations of sand and aluminous mud were 
ground out of the broken members of the Archean rocks. Several large 
rivers brought down their quota of this material, spread it out at their 
mouths, and piled it up to be farther distributed by the waves and storms 
of the ocean. Vast accumulations of clay marked the later part of the 
period during which land-locked bodies of fresh water were connected by 
narrow channels with the estuaries next the ocean. 
On the shores and in the waters of these muddy gulfs and lakes proba- 
bly lived the Jurassic Dinosaurus, the Pleuroccelus nanus, Pleurocerus 
altus, Allosaurus medius and the Ceelurus gracilis, whose remains have 
recently been described from the clays of Prince George’s county by Prof. 
Marsh. To these we may add the Astrodon Johnstonii of Dr. Leidy, and 
the crocodiles and turtles whose bones have been taken from other parts 
of the same beds. 
On the land flourished a richly varied and abundant vegetation, with 
forests, fern brakes, and trailing vines, while in the rivulets fresh-water 
plants spread over the bottom of shallow channels. 
Following this came the Albirupean, a more decidedly marine forma- 
tion, in which sands form the chief element of deposition, and which, 
later, became a distinctly sandstone-forming epoch. Layers of siliceous 
plastic mud were spread out over the indurated sands and bound them 
together in heavy belts of stone. Steady deposition, in wide irregular 
basins, gradually increased the sedimentary beds and quiet periods allowed 
the development of aquatic animals. Accordingly in the sandstones of 
this area we find the burrows of worms, the stems of encrinites, the cells 
of corals and the shells of brachiopods. On the land an ample vegetation 
must have existed, since between the layers of an upper bed of clay the 
densely packed lignitic remains of coniferous trees and the fragments of 
twigs, buds, leaves and seeds of several kinds of plants are found in 
abundance. On the south-eastern border of this zone of sand and sand- 
