Acidic Eru[)fives of Xorfheaatern Maryland. — Ke//es-. 45 
tion. The feldspars of this rock are both alkaline and lime- 
soda varieties, with a marked development of potash feldspar 
in the form of microeline. The feldspars show conspicuouslj' 
the effects of great squeezing and crushing, which, combined 
with the same chemical alteration, have given rise to a con- 
siderable development of the albite mosaic. 
The Port Deposit granite-gneiss carries a considerable 
amount of allanite which is invariably mantled by epidote, 
the two forming isoraorphous intergrowths. The epidote thus 
formed is regarded as original, as has been thought probable 
in the case of similar occurrences in the granites farther south 
in the vicinity of Baltimore. 
In regard to the staurolitic mica schist which forms a long 
narrow belt separating the Rowlandville and Port Deposit 
areas, Dr. Grimsley is inclined to the view that it was origi- 
nally a sedimentary deposit, more ancient than the granites 
and that it probably owes its highly crystalline character to 
contracting metamorphism produced b}' them at the same time 
of their eruption. 
Attention is called in the memoir to the economic value of 
the Port Deposit rocks, but more on this point might have 
been said. The quarries furnish about one-half of the entire 
amount of granite obtained in the state of Maryland. The 
stone has been taken out in commercial quantities for more 
than three-quarters of a century. The output of the Port De- 
posit quarries alone during 1892 was nearly eighty thousand 
tons, valued at almost half a million of dollars. As a building 
stone it is very durable, and according to the test made by the 
United States engineers it withstands a crushing strain of 
over eighteen thousand pounds per square inch. 
Among the structures built of this rock, as may be gleaned 
from the Maryland hand-book, may be mentioned fortress 
Monroe and the artificial island opposite it on which was erected 
fort Wood, forts Carrol and McHenry, near Baltimore; fort 
Delaware, the sea-wall at St. Augustine, Florida ; the navy 
yard and dry dock at Portsmouth, Virginia ; the Naval Acad- 
emy at Annapolis, Maryland; the foundation of the Treasury 
building, the Philadelphia, Washington and Baltimore rail- 
road stations and Saint Dominick's church at Washington; 
also the bridges over the Susquehanna at Havre de Grace 
