J. W. JUDD ON THE SECONDAKY ROCKS OP SCOTLAND. 677 



removed by denudation, except these three small islets lying midway 

 between the northern extremity of Skye and the Lewis. 



The general relations of the volcanic rocks to the Mesozoic strata in 

 the Shiant islands are exhibited in the accompanying section (fig. 6). 



Pig. 6.— Secondary Strata of Inferior- Oolite age entangled between 

 two intrusive sheets of Dolerite, Garaveilan, Shiant Isles. 



a. Coarse dolerite, forming massive columns. 



b. Inferior-Oolite shales and sandstones greatly altered. 



c. Dolerite imperfectly columnar. 



Of the third method by which relics of the Mesozoic period have 

 sometimes been preserved — namely, the inclusion in volcanic agglo- 

 merates of fragments of Secondary rock torn from the sides of the 

 vents and brought to the surface by explosive action — we have many 

 examples, especially in the case of the island of Mull, some of which 

 I have alluded to in a former paper. These fragments not unfre- 

 quently contain fossils, and thus, like the similarly ejected masses 

 found in Vesuvius and other recent volcanos, furnish clear evidence 

 of the nature of the age and character of the rocks through which 

 the igneous vents have been opened and on which the volcanic 

 cones have been piled up. 



From this description of the various conditions under which the 

 patches of Secondary strata have been preserved for our study, it will 

 be clear that the work of investigating their age and their relations 

 to one another, though full of promise, is, nevertheless, attended 

 with very considerable difficulty. 



The Secondary strata of the west coast of Scotland are found lying 

 sometimes upon the Torridon Sandstone, at others upon the great 

 gneissic series of the Highlands — now usually referred to the Silu- 

 rian. Occasionally, as on the south side of the island of Mull, they 

 may be observed resting directly upon the volcanic rocks and con- 

 glomerate beds of the Old Red Sandstone period ; while in one very 

 interesting case, that of the Innimore of Ardtornish referred to above, 

 I have detected them reposing on strata of Carboniferous age. It is 

 clear, from the unconformable relations of these Mesozoic strata to 

 all the older series of rocks, that disturbances and denudation on the 

 most enormous scale must have preceded their deposition. 



