10 THE GEOLOGY OF BERMUDA. 
shore the calcareous sands resulting from the disintegration of shells 
and corals, precisely as in other places the waves sweep up the silicious 
sands of an ordinary beach. The beach sand-rock is therefore formed 
chiefly between the levels of low and high tide, though the action of 
storms may cause it to extend somewhat above the ordinary high-tide 
level. The drift sand-rock is formed by the action of winds seizing the 
dry sand at the upper margin of the beach and transporting it further 
inland and to greater elevations. The drift sand-rock may therefore be 
formed at any level, from that of high-tide upward. The cement which 
converts all these fragmental deposits into solid rock is formed by the 
solution of the calcareous particles themselves. 
A most important step in the investigation of the history of a coral 
island is the recognition of the respective distribution of these three 
kinds of rock. The discrimination of the true reef-rock from the sand- 
rocks is not usually a difficult task. The reef-rock, whether fossilifer- 
ous or not, is usually readily distinguishable by the impalpable com- 
pactness of parts of the mass, resulting from the consolidation of the 
finely triturated coral mud; while the sand-rocks, even when appearing 
quite compact, will almost invariably reveal on closer examination their 
arenaceous texture. 
The discrimination of the two kinds of sand-rock from each other is 
much more difficult. Indeed, no absolute criteria exist for the diserimi- 
nation of beach-rock and drift-rock, though serviceable indications may 
be obtained from the texture, lamination, and fossil contents of the 
rocks. The beach-rock is, on the average, of coarser grain than the 
drift-rock, as the wind sweeps along chiefly the finer sands; but some 
specimens of the drift-rock are coarser than some specimens of the 
beach-rock. The beach-rock is, on the average, more perfectly consoli- 
dated than the drift-rock, but in this character also both rocks vary 
widely. Drift-rock, when submerged by a subsidence subsequent to 
its deposition, may come to assume the degree of consolidation usually 
observed in beach-rock. On the south shore of the Main Island, near 
Spanish Rock, I observed strata perfectly continuous dipping towards 
the water, exceedingly hard at the margin of the water, but becoming 
considerably softer as they were traced upward and landward. Mr. 
Ebenezer Bell, who some years ago had charge of some works in prog- 
ress on Boaz Island, informed me that he found that rock so soft as to 
crumble in one’s fingers became quite hard on immersion for a week or : 
a fortnight in sea-water. Some of the hardest rock which I observed in 
