GREAT VARIETY OF THESE. 133 
the springs.* A large assortment of various kinds 
of slate, lime, and sandstone may be collected from 
the beds of our rivers at those spots where in con- 
sequence of aneddy, accumulations of their products 
are heaped up. On the shores in some spots are 
found numerous pebbles fallen from the “ diluvium” 
on the incumbent cliffs, to which I have before 
alluded, but in addition to these, fragments are 
washed up from the depths far out and lodged 
amid the immediate products of the shore ;—red 
sandstone of various degrees of hardness, greywackeé 
slate, clay-iron stone, basalt, trapp, occasional 
blocks of conglomerate, porphyry, limestone, &c. 
are therefore the pebbles most commonly met with 
on the strands, and besides those masses coming 
under the denomination of pebbles, there are in 
some spots a number of blocks of considerable 
bulk piled up as it were in rude aggregation, the 
consequence of storms of a power and violence 
incalculable. The mere accumulation of these is 
not however so remarkable as the fact of their being 
usually so jamed in and locked together as to be 
quite fixed, and it is well known that where they 
are thus confined, it would be requisite to break them 
* In respect of the force of rivers at their junctions with the sea, 
few perhaps are aware of the immense power which they exercise 
throughout their entire depth and even more at the bottom than 
at the surface; the swiftness and force are also augmented when 
the passage is narrow. The power of the tide at “ Cremill 
Passage” is well known, and owing to the constant scouring which 
it effects, there is greater depth of water there, than in any part 
of Hamoaze or of the Sound, The matter however which the 
tide was wont to bear outwards to the body of the sea is now by 
the erection of the Breakwater intercepted, and whereas Plymouth 
Sound had once a gravelly and sandy bottom in all directions, 
the channel is now gradually being choked up towards the 
middle by a bank of mud corresponding to the breadth of the 
structure which now crosses it. 
