STATHAM — ON THE GEOLOGY OF THE SCILLY ISLES. 13 



in latitude 49° 57' N., and in longitude 6° 43' W. bearing west hj 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, Bryer, 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 granite, and that, in dredging the sea-bottom between these two 

 points, shells and 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 

 narrow 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 100 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 



