174 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
through in every direction with needles, which are colorless, brown, 
black, highly refracting, when light colored, and are probably rutile. 
In other instances, there are bright, highly refracting, colorless little 
crystals that closely resemble and are believed to be zircons. Of all 
the inclusions, by far the most abundant are irregular-shaped, round, 
columnar, and dihexahedral bright little bodies, each usually surrounded 
by a dark rim. They occur single, or arranged in lines or groups. 
Some contain a single, movable bubble, and are liquid inclusions con- 
taining a gas bubble. The bubble in a few cases was found to move 
spontaneously, and to be constantly in motion. Others contain two or 
more bubbles, and are then believed to be glass inclusions. The dihexa- 
hedral bodies are negative quartz crystals, or holes having the shape 
of a quartz crystal. 
As to the bearing of the facts on the question of the origin of the 
material from which these sandstones were formed, it may be said that 
besides quartz, two constituents occur, one, feldspar, common to all 
granites, and the other, biotite, belonging to certain classes of granites. 
The quartz itself furnishes in its liquid and glass inclusions evidence 
of its deep-seated origin and of its formation from a molten magma 
under considerable pressure. This follows if the inclusions are, as is 
believed, glass inclusions, and if the liquid inclusions contain gas bubbles, 
such as carbon dioxide or some gas requiring pressure for liquefaction. 
Besides, all the inclusions found in the quartz grains are quite character- 
istic of and common in quartz grains found in granites and other rocks 
formed at great depths and under considerable pressure. It is true that 
both rutile and zircons are found in metamorphic schists, the former 
being more characteristic of schists and other metamorphic rocks than 
of rocks which are believed to have solidified from a molten magma. 
Заб the glass inclusions certainly furnish evidence of crystallization from 
a molten magma, and this, taken together with the liquid inclusions with 
a gas bubble, make it quite probable that the material for the formation 
of these sandstones is furnished by the disintegration of a granite or some 
rock formed under similar conditions. 
THE Origin OF THE CEMENTING MATERIAL. 
I conceive of four possible sources of the lime carbonate with which 
the reef rocks are hardened, as follows : — 
1. Dissolved by rain-water or spray from the beach sands them- 
selves; that is, carried from the upper layers of the sand and deposited 
in the lower ones, 
