164 Notices of Memoirs — Notes on Rockall Island and Bank. 



station. But minute as it is in size, and exposed as it is to the full 

 swell of the Atlantic, whicli rises and falls there more than 12 feet 

 in the calmest weather, such use of the rock appears to be out of the 

 question. Indeed, fishermen and sailors from men-of-war have only 

 occasionally effected a landing upon it, under the most favourable 

 conditions, with the greatest difSculty. The rock lies out of any of 

 the usual tracks followed by steamships and sailing vessels in crossing 

 the Atlantic. At a distance it appears, with its dark-coloured base 

 and top whitened with the dung of innumerable sea-fowl, so like 

 a ship under full sail, that in war-time the captains of men-of-war 

 are said to have been frequently deceived by it. 



Although no landing was effected during the recent investigation 

 of Rockall, the exploring party managed to secure a number of 

 interesting drawings and photographs of the rock. The Eev. "W. S. 

 Green describes the general character of the mass in the following 

 words : — " The east face seemed like a great slab of gray granitoid 

 rock (and I was within 20 yards of it), with rectangular joints broken 

 off at the north, so as to show the square edge of another slab, and 

 this was in turn broken oif, showing the face of a third." This 

 granitoid mass "rests on a rock showing a kind of bedding or 

 jointing (?), dipping about east, and at an angle of 30° or so." 



So far as is known, no specimens have ever been obtained from 

 this underlying mass on the west or south-west of the rock, and it is 

 impossil)le to say whether it consists of sedimentary materials, of 

 stratified tuffs, or of some fissile igneous rock. 



Of the overlying granitoid mass, however, the relations of which 

 seem to strikingly resemble those of an intrusive sheet, the inde- 

 fatigable exertions of Professor T. Eupert Jones have resulted in 

 bringing together three specimens. These have been submitted to 

 Professor Judd for examination in the Geological Laboratories of the 

 Eoyal College of Science. One of these specimens was obtained by 

 Basil Hall as long ago as the year 1810, when Eockall was visited 

 by H.M.S. " Endymion " ; the others were obtained by Commander 

 Hoskyn and Captain Inskip respectively, during the visit of H.M.S. 

 " Porcupine " to the rock in 1862. In each case the specimens were 

 obtained by an active sailor, with a line attached to him, springing 

 from a boat on to the rock, and, when he had secured fragments of 

 it, throwing himself into the sea to be towed back to the boat. 



Two of the specimens were found on microscopic examination to 

 be distinctly granitic in structure, the quartz, felspar, and augite of 

 ■which they are made up being allotriomorphic. Their structure, 

 however, resembles that of the granite-porphyries rather than that 

 of the true granites. The third specimen, while made up of the 

 same minerals, is distinctly hypocrystalline, having the kind of 

 groundmass which Eosenbusch distinguishes as ' hypidomorphic' 

 This variety, having a darker colour, as well as a finer texture, may 

 not improbably form veins, or possibly inclusions, in the main mass ; 

 or it may belong to the edge of the intrusive sheet. All the rocks 

 are somewhat drusy or miarolitic in structure. 



Detailed microscopical examination shows that the material of 



