J. W. JUDD ON THE SECONDARY ROCKS OE SCOTLAND. 667 



isolated fragments of the Secondary strata are now revealed to us ; 

 and, except where protected by the harder and less perishable vol- 

 canic rocks — either bnrying them under enormously thick accumu- 

 lations of lava or entangling them between igneous sheets — almost 

 every vestige of the Mesozoic strata has been removed by the 

 denuding forces. Nevertheless, wherever portions of the great 

 basaltic plateaux have escaped being swept away by the denuding 

 forces, as in the islands of Muck and Eigg, there masses of the 

 Secondary strata are found cropping out from beneath them ; while 

 around the igneous centre of Ardnamurchan, and perhaps also that 

 of Rum, the same strata, metamorphosed indeed almost beyond 

 recognition, are found entangled between igneous sheets and inter- 

 sected by a plexus of dykes. 



I cannot here refrain from citing a vivid illustration of the 

 manner in which the preservation of these curiously isolated frag- 

 ments of the Mesozoic deposits has been effected, which was sug- 

 gested to me by the late Sir Henry James a few years ago, when I 

 had an opportunity of conversing with him upon the subject. He 

 compared the fragments of such strata, which have escaped removal by 

 denudation, to the little bits of paper that would escape being washed 

 away if a newspaper with a number of heavy stones on it were laid 

 in the bed of a running stream. 



The isolated patches of Secondary strata are now found widely 

 scattered over an area measuring 120 miles in length from north to 

 south, and 50 miles in breadth from east to west. Within these 

 limits, however, such patches occur only where those peculiar con- 

 ditions have prevailed which, as we have shown, have determined 

 the preservation of these fragmentary relics — namely, in proximity 

 to the great Tertiary volcanos of Skye, Rum, Ardnamurchan, and 

 Mull. Thus the whole northern part of the island of Skye consists 

 of a plateau of basaltic lavas poured out from the volcanic centre of 

 the Cuilin Hills ; all round the edges of this great basaltic plateau 

 the Secondary rocks, which they have overwhelmed, can be traced 

 here and there in cliff-sections ; and at a few points in the interior, 

 where valleys have been cut deeply into the plateau, inliers of the 

 same Mesozoic deposits make their appearance. From the careful 

 study of the phenomena presented at these various points, it becomes 

 clear that the denuded surfaces of these Secondary rocks formed the 

 terrestrial areas on which the lavas were poured out. In Raasay 

 the same relations are exhibited in an equally striking manner, the 

 Secondary rocks making their appearance all round the shores of the 

 island, under the covering of Tertiary lavas which forms its higher 

 portions. Even where the most minute isolated patches of the Ter- 

 tiary lavas occur, as at Strathaird and Ru-Geur in the southern 

 part of Skye, the Secondary rocks are found to be preserved 

 beneath them. Still more strikingly is this found to be the case in 

 Mull, where patches of Secondary strata can be traced at short 

 intervals all round the shores of the island and in the adjoining 

 district of Morvern, in such a manner as to lead to the irresistible 

 conviction that the great volcano of that district was opened in the 



