482 CLARK AND BIBBINS 
with cobble stones. Frequently the sands pass over into sandy 
clays and these in turn into more highly argillaceous materials 
which are commonly of light color, but at times become lead- 
colored, brown or red, and not unlike the variegated clays of 
the Patapsco formation. Those arenaceous materials which lie 
adjacent to ferruginous clays are not infrequently indurated by 
hydrous oxides of iron, forming ferruginous sandstone. The 
more arenaceous deposits are commonly cross-bedded, and the 
whole formation gives evidence of rapid deposition. 
The strike of the beds is in a general north-northeast south- 
southwest direction, corresponding to the eastern border of. the 
Piedmont Plateau. The dip of the strata, so faras can be deter- 
mined from the narrow exposures which have been obtained, 
is probably between thirty and forty feet to the mile. The 
irregular character of the sedimentation, together with the small 
areal extent of the deposits, renders it very difficult to make any 
satisfactory measurement. 
The thickness of the Patuxent formation is rather variable, 
but, so far as has been determined, has not been found to exceed 
150 feet, although it may be considerably thicker at some points. 
Characteristic local sections-—The deposits of the Patuxent 
formation outcrop, among other places, in the valley of the Little 
and Big Patuxent rivers, having been reached in the iron-ore 
openings which have been made at many points in the overlying 
Arundel formation. An excellent section is found in a cutting 
on the Baltimore and Ohio Railroad a short distance to the 
south of Contee. At the latter locality the coarse gravelly 
phase of the formation is well developed, and is unconformably 
overlain by the iron-ore clays of the Arundel formation. At the 
southern end of the cut the gravels have become cemented near 
the contact with the Arundel into a considerable ledge of con- 
_glomerate, by the leaching into them of the hydrous oxide of 
iron from the overlying deposits. 
One of the most comprehensive sections of the Patuxent 
formation is at School House Hill, Baltimore county, about three- 
quarters of a mile northwest of Lansdowne on the Baltimore and 
