40 AN INVESTIGATION INTO THE 
GRANITE, WESTERLY, RHODE ISLAND, UNITED STATES. 
This rock is a fresh, very fine grained, massive, pale pink granite, being much 
finer in grain than the other granites referred to in this paper. 
Under the microscope it is seen to be composed essentially of biotite, micro- 
cline, orthoclase, and quartz. In addition to these constituents a small per- 
centage of plagioclase and a few grains of magnetite are present as accessory 
constituents, together with a little chlorite and muscovite as alteration 
products. 
The feldspars form the greater part of the rock, microcline being by far the 
most abundant of these. It shows in a striking manner the characteristic 
cross-hatched twinning of this species, and is usually quite fresh. The ortho- 
clase in untwinned individuals is frequently distinctly turbid from the 
development of kaolin, and in a few places muscovite in larger individuals can 
be seen inclosed in it, apparently developing as a secondary product at its 
expense. 
The quartz, which is next in abundance, usually shows marked undulatory 
extinction, and some grains have been so strained that they fall into areas with 
distinctly different optical orientations. The quartz, instead of occupying 
corners between the feldspar individuals, usually occurs as subangular or 
more or less rounded grains associated with the feldspar, and apparently 
more nearly contemporaneous with this mineral in its crystallization than 
is usually the case. The rock often shows a tendency to granophyric struc- 
ture, small rounded grains or vermiform inclusions of quartz being sometimes 
seen in the microcline. The structure otherwise is of the normal granite type. 
The biotite is very subordinate in amount and is more or less changed into 
chlorite. 
Although these decomposition products are present, the rock can not be con- 
sidered as one which has undergone much alteration. It has, as a matter of 
fact, undergone very little, and is to be classed as a distinctly fresh rock much 
fresher than granites usually are. 
A color-process photograph of the rock is seen in Plate VIII A and a photo- 
micrograph of a thin sectiorl taken between crossed nicols in polarized light 
and magnified 30 diameters is shown in Plate VIII B. 
Four test pieces were used in measuring the elastic constants, viz, two square 
prisms, a and b, and two round columns, c and d. Two sets of determinations 
were made on each of the first three specimens, the instruments being attached 
to different pairs of sides in each case, and four sets of determinations were 
made on specimen d in planes making angles at 45 with one another. Ten 
determinations of vertical compression and three of lateral extension were 
thus made the results of which are given in the following table : 
