1890 .] 
127 
[Crosby. 
been derived chiefly from the disintegration of the coarse granite 
north of Boston, and crystals of feldspar are often seen adhering 
to the quartz, which thus passes into subangular or glaciated frag- 
ments of granite. 
Sand . — As we pass from the coarsest gravel to the finest sand the 
most important facts to be noted are : (1) the rapid increase in the 
proportion of quartz in its different forms, and (2) the concomitant 
change from distinctly glaciated to simply subangular forms. In 
the coarser gravel, as already noted, the quartz is chiefly in the 
form of quartzite and sandstone, only occasional fragments appear- 
ing to have resulted from the breaking up of veins of quartz ; 
while in the fine gravel the quartz grains are mainly clear and 
vitreous and evidently due, as explained, to the breaking up of 
coarse granite. The coarse sand consists chiefly of limpid and 
milky quartz, which is probably due in part to the comminution of 
quartz veins, but mainly to the complete or nearly complete disin- 
tegration of granite and also of quartzite and sandstone ; while 
the medium and especially the fine sand are almost pure limpid 
quartz, the source of which we can only conjecture in most cases, 
in subangular to more or less rounded grains. The quartz grains 
are often colored, not coated, with iron oxide (ferruginous), and 
very rarely a grain is amethystine. The coarse sand contains an 
appreciable and sometimes an important proportion of comminuted 
diorite, slate, etc. ; and in all the sand, but especially the coarsest, 
there are occasional or frequent fragments of feldspar (chiefly pink 
orthoclase) often still attached to grains of quartz and always 
showing hard, fresh cleavage surfaces. Such comparatively rare 
minerals as epidote and garnet are observed semi-occasionally ; 
but the only important or constant constituent of the sands not 
yet mentioned is the black oxide of iron. This is always present 
and is relatively more abundant, or at least more conspicuous, in 
the finer grades. It comprises both magnetite and menaccanite, 
and the latter, judged by the magnetic test, is decidedly the most 
abundant. Although the iron oxides are frequently attached to 
grains of orthoclase or quartz, it is certainly probable that they 
have come chiefly from basic rocks, like diabase and diorite. Since 
the sands consist almost entirely of hard, angular grains of quartz, 
which have resisted or eluded the wearing action of the glacial 
movement, we find that the typical sands and gravels are as strongly 
