Reports cO Proceedings — Geological Society of London. 237 



Professor J. W. Judd, C.H., F.R.S., gave the following general 

 accoutit of the geology of Kockall ' : — 



Eockall is a small isolated rock in mid-Atlantic, lying 184 miles west of 

 St. Kilda ; it has a circumference of only 100 yards and a height of 70 feet, 

 and, except in the very cahnest weather, is quite inaccessible. It is the haunt 

 of sea-birds and, with its whitened top, resembles a sailing ship, for which it 

 has often been mistaken. The rock rises from a bank (the ' Eockall Bank ') 

 upon which there are several dangerous reefs. 



More than 300 years ago it was reported that a large island occupied the site 

 of Eockall, and, for a hundred years or more, all Atlantic charts represented 

 this island, which was named ' Busse Island ', with a number of other islands 

 and islets, as present in the North Atlantic. Taking these supposed facts in 

 connexion with the famous classical stories of an 'Atlantis', the theory was 

 often advanced that the North Atlantic was an area of subsidence, and that 

 the reported islands — and, in the end, Eockall — were the last vestiges of the 

 famous vanished continent. Modern research has, however, quite disposed of 

 this theory. 



Nevertheless, Eockall is of considerable interest, especially to geologists. 

 In 1810 Basil Hall, then a young officer in H.M.S. Endymion, obtained 

 a fragment from this rock, which later found its way into the collection of the 

 Geological Society. More than thirty years afterwards the specimen was 

 recognized ; it was then mislaid for another thirty years, and in 1895 was 

 brought to me by the late Professor T. Eupert -Jones. 



He not only carefully studied all the literature connected with Eockall, 

 but was able to trace two other specimens of the rock, the loan of which 

 he obtained and brought to me. They had been procured by two of the 

 officers of H.M.S. Porcupine in 1868 during the survey of the North Atlantic. 

 The microscopic study of these specimens shows that in Eockall there exist 

 rocks of exceptional interest, which are not represented in our Islands, but 

 have analogies in the Christiania district of Norway, where they have been 

 so well studied by Professor W. C. Brogger. These rocks, as shown by 

 microscopic study and by a chemical analysis made by Mr. Makins, consist 

 essentially of three minerals — quartz, the felspar albite, and the rare soda- 

 pyroxene oegirite, with its dimorphous form acmite. The rock, therefore, 

 resembles the soda-granite and the grorudite of Professor Brogger, but, in 

 deference to the opinion of the distinguished Norwegian petrographer, a distinct 

 name was given to it. 



In 1896 an attempt was made to obtain further specimens of the rocks of this 

 islet by members of the Eoyal Irish Academy ; but, although many valuable 

 observations were recorded, it was found, after two voyages had been made to 

 Eockall, quite impossible to land and obtain specimens. 



Dredging operations have yielded many specimens from the Eockall Bank, 

 and these were examined by the late David Forbes and Professor Grenville A. J. 

 Cole. The abundance of basalt fragments among these dredgings suggests 

 the possibility of Eockall belonging to the same petrographical province as 

 St. Kilda, Iceland, the Inner Hebrides, and the North of Ireland ; hitherto, 

 I believe, no rocks resembling ' rockallite ' have been found in this province. 

 On the other hand, the existence of borolanite and other alkaline rocks in 

 the Northern Highlands suggests the possibility of Eockall being the western 

 extension of a much older province, which includes the Christiania district 

 and the Scottish Highlands. 



Some months ago Professor Iddings and Dr. Washington represented to me 

 the desirability of a more detailed analysis of this rock. One of the two small 

 fragments available was, by the advice of Professor Watts, sent to America by 

 the Council of the Imperial College of Science and Technology, to whom they 



^ For an account of "Eockall Island and Bank" see Geol. Mag., 1899, 

 pp. 163-7, and Trans. Eoy. Irish Acad., vol. xxxi, pt. iii, pp. 39-98, 

 pis. ix-xiv, 1897. 



