1888. ] AT [Uhler. 
red or white clay, which in turn grades into sandy clay and sand, from 
sixteen to thirty feet in thickness; this is overlaid by five to ten feet of 
ferruginous sand, carrying more or less pebbly, compact quartz, and 
this in turn is capped by the ferruginous sandstone ranging from two to 
twenty feet in thickness, over which, more or less, ferruginous sand, peb- 
bles and gritty material, usually only a few feet thick, extends up to the 
soil of the surface. Accompanying this upper sandstone small and mode- 
rately large boulders of all the varieties of our adjacent Archean rocks, 
but particularly of the flaky quartz, similar to that from the mica schists, 
occur, and sometimes form thick beds in the neighborhood of old river or 
brook channels. 
So, by adding together the various members enumerated above, we 
reach an aggregate of more than two hundred feet for the full thickness 
of this formation, as we recognize it at the present time. 
It rests below the green sand of the Cretaceous, which on the western 
shore of Maryland is piled up on a ferruginous sand-crust of its own ; but 
the Albirupean has a much steeper average dip than the Cretaceous, and 
passes unconformably beneath it, as may be seen in the cliffs of the Severn 
river near Round bay. 
The Albirupean dips eastwardly about ten to twelve degrees, while the 
dip of the Cretaceous scarcely exceeds five or six degrees. 
Tt is nevertheless a fact that abrupt dips occur in all the alluvial forma- 
tions of our tide-water region, but these appear to be due to the wavy in- 
equalities of the underlying beds in places where material has been heaped 
up into hillocks by the arrest of rapid, loaded currents of water. 
A similar kind of deposition of loose material takes place at the present 
time, on the bottom of Chesapeake bay and insthe mouths of rivers like 
the Magothy, where ‘mud lumps,’’ so-called, accumulate at the points 
where currents of water meet. 
Thus far but few kinds of fossils have been discovered in the Albirupean 
belt, and these have rarely been found perfect enough for identification. 
Still, we have one species of Brachiopod, stems of Ecrinites and an An- 
nelid-buirrow in the white sandstone, and many unidentified vegetable 
forms in the dark clays which overlie the sandstone. 
Such are a few of the features which characterize the Albirupean forma- 
tion of the State of Maryland. But our sketch would be incomplete if it 
omitted to notice some of the peculiarities of the great clay-formation 
which lies beneath the Albirupean. Both together have been united in a 
common term as forming what has been called the Jurasso-Cretaceous. 
But whatever their geological position may be in correlation with the 
European formations, we are now accumulating information enough to 
show that they have points of difference from those which have been 
commonly admitted, and to render it necessary to symbolize them by dis- 
tinct names. It is with this view that the term Albirupean is here pro- 
posed for the great sandrock system lying beneath the greensand Creta- 
ceous, and the term Baltimorean for the conspicuous clay formation which 
