9 
Uhiler. } 42 [Jan. 6, 
The Albirupean Formation and its nearest relatives in Maryland. 
By Pe i. Unter, 
(Read before the American Philosophical Society, January 6th, 1888.) 
Near the mouth of the Patapsco river, almost in the path of its ship 
channel, and at a distance of nearly one mile from the nearest shore of 
Rock creek, there projects above the surface of the water a huge pile of 
compact siliceous rock. This conspicuous body of sandstone has been 
an object of interest to mariners and tourists ever since the entrance to 
the harbor of Baltimore was first discovered. Almost from the first set- 
tlement of the region this island of stone has been called the ‘‘ White 
Rocks.’’ This name was given to it because of the white color which it 
presents when seen from the channel of the river in clear daylight; and 
the plural term, rocks, has reference to the several masses inte which the 
island has been split by natural agencies. No accurate description of this 
remarkable object has yet been published, and as it is directly connected 
with one of the great geological features of Maryland, it deserves to be 
particularly noticed. 
This white quartzite now forms fragments of the great sand-belt which 
crosses Chesapeake bay from the vicinity of Elkton in Cecil county, and 
runs in-a south-west direction to beyond the great Patuxent river and 
grades into the low hills before reaching the East branch of the Potomac 
river. Kleven miles north-north-east of the city of Baltimore, it consti- 
tutes an extensive superficial bed, projecting two or three feet above the 
surface of the sandy loam, exposed over more than half an acre in extent. 
At this point it is broken into blocks and chunks, is largely composed of 
pebbly conglomerate (the pebbles often angular in form), and extends 
down fully ten feet into the sandy loam. South-east of this point for a 
distance of three miles or more, the same variety of rock has been reached 
at a depth of twenty to twenty-five feet in the excavations made for 
wells. . 
The next point where this quartzite may be seen is about eleven miles 
farther southeast. There much of the rock has an exceedingly dense tex- 
ture. It lies in a broad sloping sheet dipping about ten degrees towards 
the east-south-east, and appears to be about twelve feet in thickness. This 
sheet of rock runs beneath tidewater at the mouth of Back river, and 
seems to cover nearly an acre in superficial extent. 
About one mile farther to the west and up the Back river a continuation 
of this bed makes its appearance on the sloping shore. 
The rock next appears in North Point creek about five miles farther 
southward, still maintaining the same compact texture. From this place, 
however, much of it has been removed, because of its obstruction to 
navigation. 
Three miles distant, across the channel in the Patapsco river, we reach 
the island of stone alluded to at the beginning. 
