STATHAM — ON THE GEOLOGY OF THE SCILLT ISLES. 13 
in latitude 49° 57' N., and in longitude 6° 43' W. bearing west by south 
from the Land's End, and due west from the Lizard ; from the former 
point they are distant little more than twenty-seven miles in a direct 
line, though the distance from Penzance pier, the usual starting-place 
of the vessels from the mainland to St. Mary's Pool, is about forty 
miles. So far from being mere rugged rocks, these islands afford a 
pleasant home to between two and three thousand inhabitants, the 
total population having been computed in 1851 at 2,601 souls, the 
majority of whom dwell upon St. Mary's, although five of the other 
islands — viz., Tresco, St. Martin's, St. Agnes, Bi-yer, and Sampson's — 
have a scattered population upon them nearly in proportion to their 
relative size. As the character of the rocks, being almost exclusively 
granitic, is very similar to that of the extreme promontory of Corn- 
wall, it has been suggested by some writers that they may have been 
originally united to the mainland, and traditions are not wanting, of 
a very ancient date, which might serve to confirm this opinion, were 
there not many countervailing reasons to be alleged in opposition. 
From the circumstances that the Gulf, or Woolf Rock, which lies 
midway between Scilly and Land's End, is of greenstone, and not 
of gi'anite, and that, in dredg'ng the sea-bottom between these two 
points, shells anl sea- weeds have been occasionally brought up 
clinging to greenstone, or clayslate, it is conceived that a tract of 
metamorphic rocks exists beneath the ocean between the mainland 
and the Scilly Isles, and that the latter are thus outliers only of 
the great granitic range of Devonshire and Cornwall. Many circum- 
stances tend to prove that the conformation of the islands is very 
different now from what it has been at a former period, within even 
historic times. Local tradition asserts that anciently there was a 
naiTOw causeway by which persons could pass across Crow Sound from 
St. Mary's to St. Martin's, and the ledge of rock which is visible at 
low water a little below the surface in this part is still called the 
" Pavement." Then, again, the Gugh, which, in the time of Borlase 
(about 1 00 years ago), was described as " a part of Agnes, and never 
divided from it but by high and boisterous tides," is now at each period 
of spring-tides an island, and there is then sufficient depth of water 
in mid-channel for a boat to shoot across the bar. These considera- 
tions would seem to show that there has been a decided sinking of the 
