166 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 
According to the returns furnished by the special agents in the em- 
ploy of the building-stone department of the Tenth Census, there were 
during the years 1880~82 some eighty-three quarries of various kinds 
of building stone in the State, situated chiefly either immediately on the 
coast or within easy reach of tide-water. The product of these quarries, 
as may readily be imagined by one at all acquainted with the geological 
features of the State, is largely granitic; slate is, however, quarried 
quite extensively in the eastern part of the State (Piscataquis County), 
and quarries of diabase are worked in a few cases. All the varieties 
of rock at present regularly quarried and used for building purposes 
may be classed under the following heads: 
Biotite granite. 
Biotite muscovite granite. 
Hornblende granite. 
Hornblende biotite granite. 
Biotite gneiss. 
Biotite muscovite gneiss. 
Diabase. 
Olivine diabase. 
Argyllite or slate. 
Representative specimens of all these varieties have been received at 
the National Museum and properly dressed for purposes of exhibition 
and comparison. Thin sections have also been prepared and submitted 
to microscopic examination, with the results given in the following 
pages. It is perhaps to be regretted that tests of the compressive 
strength of these stones could not have been made in this connection. 
It is, however, safe to say that, so far as can be judged from the speci- 
mens received at the Museum, any and all of them are of sufficient 
strength for all ordinary purposes of construction. There is, indeed, 
scarcely a poor stone in the collection, although of course some are 
much better than others. 
GRANITE. 
Of the eighty-three quarries already mentioned seventy-four are of 
granite or gneiss. All the Maine granites, so far as observed, are com- 
posed of three principal minerals, quartz, orthoclase, and plagioclase,* 
besides which there is always present, in such abundance as to give spe- 
cific character to the rock, one or nore of the minerals muscovite, bio- 
tite, or hornblende, while apatite and magnetite can nearly always be 
detected in microscopic proportions. As a common though not so con- 
stant an accessory, there is also frequently present, in quantities so 
small as to require the microscope for their determination, one or more 
* No attempt has been made to determine the exact species of triclinic feldspars in 
these rocks; hence they are referred to (microcline excepted) under the general term 
plagioclase. 
