180 JOURNAL OF THE PLYMOUTH INSTITUTION. 
The different layers exhibited varying degrees of cohesion. The 
upper beds, in the main, were crumbly, but consolidated patches were 
of frequent occurrence. The lower beds were at points so solid 
that they defied the pick, and had to be broken up by blasting. 
Here and there the layers of smaller pebbles appeared to have been 
considerably influenced by pressure, having assumed an aspect of 
remarkable solidity, in which the individuality was partially lost. 
The main cause of cohesion was, however, the infiltration of water 
charged with carbonate of lime from the limestone bluff. 
The most remarkable feature of the Beach was the character of 
its materials. The modern beaches of the Sound area are in the 
main formed from the rocks immediately contiguous. At the Hoe 
they are in chief part of the local limestone. Not so this ancient 
sea margin. Save in the lowest, or boulder bed, limestone was of 
quite exceptional occurrence. Pebbles of red and grey grit were 
much more frequent, and fragments of slate occasionally occurred. 
The predominant constituent was, however, the Triassic trap of 
Cawsand Bay. This is equally true of the larger pebbles and of 
the finer material classed as sand. The granitic sand spoken of by 
Dr. Moore was nowhere visible, and he was probably there in 
error. There were some granules of quartz, but of no more 
importance than the quartz pebbles and fragments to be found in 
every modern beach in the neighbourhood. 
Now the only actual beach in the locality that presents any like- 
ness to this ancient beach is that at Cawsand, two miles distant 
across the Sound, and in constitution the two may be regarded as 
practically identical. But this fact suggests a somewhat difficult 
problem. 
Undoubtedly the materials of the Raised Beach were carried to 
the Hoe from Cawsand Bay, round the eastern point of Drake's 
Island ; for a boulder of upwards of 2 cwt., derived from an 
exposure of peculiar trap rock which occurs only in the island in 
this immediate locality, was found in the basement bed. What is 
now the island then formed part of the main peninsula of Mount 
Edgcumbe. The drift to its eastern end was thus along shore, and 
easily explicable. But how did the materials cross the channel 
between the island and the Hoe 1 It is true the distance is only half 
a mile, but for a couple of hundred yards the interval is occupied 
by a portion of the deep water-trough, which reaches from near 
Mount Batten to Saltash Bridge j and the present low- water depth 
