14 THE GRANITES OF MAINE. 
53 thin sections of typical rocks for this report; Mr. E. C. Sullivan, 
of the Survey, has made 10 determinations of carbonate in granite, 
and Mr. W. T. Schaller, also of the Survey, has determined 2 min- 
erals. Mr. Wirt Tassin, assistant curator of the National Museum, 
has made an analysis and report on a new mineral from a quartz 
vein, and Dr. George P. Merrill, head curator of geology of the same 
institution, has determined a feldspar from the Waldoboro quarry. 
Mr. G. K. Gilbert, geologist of the United States Geological Survey, 
has contributed an important photograph (PL VII, A), bearing upon 
origin of sheet structure in granite, with an explanatory note. Prof. 
James F. Kemp, of Columbia University, has kindly made 1 some 
bibliographical contributions. The statistical table of granite pro- 
duction in Maine was prepared by Miss Altha T. Coons, of the 
Survey. 
The word " granites,' 1 in the - title, is used primarily in its popular 
and commercial sense, and includes also the so-called "black gran- 
ites." The proper scientific names of the rocks thus designated are 
given in the sections devoted to classification and to the descriptions 
of the quarries and their products. 
PART L— SCIENTIFIC DISCUSSION. 
GRANITE PROPER. 
GRANITE IN GENERAL. 
DEFINITION. 
Granite, in a general sense, is essentially an entirely crystalline 
igneous rock, consisting mainly of quartz, potash feldspar, and a 
feldspar containing both soda and lime, also of a small amount of 
either white or black mica or both, and sometimes of hornblende, 
more rarely of augite, or both. Where granite has, subsequent to its 
crystallization, been subjected to pressure sufficient to produce a par- 
allelism in the arrangement of its minerals — that is, a schistosity — it 
is no longer a true granite, but a gneiss or granitoid gneiss. 
ORIGIN. 
Granite is now regarded as the product of the slow cooling and 
crystallization of molten glasslike matter at a dull-red heat — matter 
which contained superheated water, and was intruded from beloAv 
into an overlying mass of rock of sufficient thickness not only to 
prevent its rapid cooling and its general extrusion at the surface, but 
also to resist its pressure by its own cohesion and powerfully to coin- 
press it by its own gravity. As carbonic acid can be liquefied only 
under pressure, its presence in liquid form within some of the micro- 
