GEOLOGY OF SCILLY. 227 



with little more than her keel above water. Nevertheless, 

 although they abandoned the wreck, their temporary aid had 

 been essential ; had they not taken her in tow, the set of the 

 current would have drifted her clear of the islands into the 

 broad Atlantic waste.* 



Granite is the substance of these islands. Generally it is 

 thought that Scilly is only a continuation of the granite of 

 Land's End ; against which conclusion the idea of a separate 

 and distinct range seems supported by the fact that, in 

 dredginff between the islands and the mainland, sea-weed is 

 often brought up attached to bits of slate and greenstone ; 

 and the Wolf Eock, which lies not far southward of a line 

 from the Land's End to Scilly, is composed of this same 

 greenstone. What geologists call " the strike " of the granite 

 here is, with few exceptions, towards the north or north- 

 north-west. The rock itself is not always confined to the 

 constituent parts of quartz, felspar, and mica : shorl is a 

 very common ingredient, sometimes accompanying the mica, 

 sometimes replacing it. Hornblende is rare, chlorite still 

 rarer. Veins of pure white quartz, of considerable size, 

 often intersect the granite ; rose-coloured quartz, and even 

 chalcedony, have been found ; but the general nature of the 

 stone is of a coarse kind, useless for quarrying ; and the gra- 

 nite needed for the new lighthouse is brought from Cornwall. 



The reader will be curious to know about the zoological 

 wealth of Scilly. Rich the place undoubtedly is, yet not so 



* For this narrative I am indebted to North's Week in the Isles of Scilly — 

 a work full of valuable details for any one who may contemplate a visit to these 

 Isles. 



