—_—_ 
THE HAWKESBURY SANDSTONE. 89 
driven inland by the wind blown up into dunes, and from which 
the whole island above water has been formed. 
The sand may be seen to be made up in by far its greater 
part of the shells of mollusca. Species of Tellina, Cardium, 
e is the case for some distance, for the same beds of sandstone 
tine of varying thickness, produce a series of very thin, hard layers 
inthe mass of sand, alternating with seams of less consolidated sand 
be are to be observed commonly on the surfaces of fresh sanc 
ons s. These layers or strata of the hardened sand follow in form 
: 0 yp ny qi 
ex,.Lt would be of great interest to determine, by careful pic 
tures ation, wha lative percentages of the "iiibiaw calcareous struc- 
, s composing the 4s of coral islands i different parts of the 
the: 1. T collected specimens of all the calcareous sands accessible se 
compeyaee of the “Challenger,” with that object. They vary much 
being satel eswcaliiters i 
+h 
oyage of 
tion, some 2 
xt The process is described by Jukes, in his account of Raines Islet, 
Voyage ofthe *Fly,”p. 3390. . 
