50 
LIMEROCK. 
black, white, and pink, often also veined and 
blotched with these conjointly, and in one solitary 
instance I have found it green. It is suspected 
greatly that to a large amount, these colours may be 
due to organic remains imbedded*in the stone, but 
though, these forms are abundantly coloured in this 
manner as if painted artificially, the very same 
colours are spread profusely through certain locali¬ 
ties of the limestone seemingly devoid of fossils. 
The ordinary breadth of the limestone tract from 
Devonport, onwards to Yealm Bridge may be esti¬ 
mated at about a half mile, and its height does not 
often exceed one hundred feet, hereby offering a 
contrast to the elevation of the slate hills, which is 
perhaps on an average three or four hundred feet. 
In connexion however with this latter circumstance, 
it must be noted, that saving the slate and sandstone 
hills directly bordering the coast at some parts, the 
land of South Devon apparently rises from the lime¬ 
stone to a low range of slate hills at its immediate 
back, and thence by gradual steps to the schist 
hills bordering the moor, which are often seven, 
eight, or nine hundred feet high, and lastly to the 
moor itself, whose prevailing elevation is still 
greater. In respect of depth , nothing decisive is of 
course known, save where it overlies other strata, 
and where it is prone to put on a very tabular con¬ 
dition ; it may with great propriety be inferred, that 
this rock passes to a very great depth, and rests 
ultimately on the general supporting bed of our 
grauwacke strata, namely granite. The top of the 
limestone range is for the most part quite level, but 
in some places, the rock assumes the “ round-back” 
form. If a geologist stand on an elvated part of 
of our limestone in the immediate vicinity of Ply¬ 
mouth, he can distinctly see, that this rock joins 
itself by a gradual rise to the slate hills, which 
back it in every direction ; he will see also, that 
