676 J. W. JUDD ON THE SECONDAKY KOCKS OP SCOTLAND. 



had the effect of placing many of the Secondary rocks far below the 

 sea-level, and thus hopelessly out of reach of at least the present 

 race of geologists. 



The examples of the relations of the Secondary rocks of the 

 Hebrides to the superincumbent lava-masses which we have already 

 given will sufficiently illustrate the first of the three methods by 

 which the Mesozoic relics have been preserved. Of the second case, 

 that in which masses of the Secondary rocks have survived to the 

 present time through being included between intrusive sheets of 

 igneous rock, we have also many striking examples. On the east 

 coast of the peninsula of Trotternish, in Skye, as was so well shown 

 by Macculloch, the sheets of dolerite are found running along the 

 planes of bedding of the Secondary strata for miles with the greatest 

 regularity ; so strikingly is this the case, indeed, that they might 

 easily be mistaken for contemporaneous lavas, but for the fact that 

 they occasionally cross the lines of stratification or send off dykes 

 and veins into the enclosing beds, which exhibit signs of metamor- 

 phic action as well above as below the intrusive sheets. Between 

 Loch Staffin and the Kilt rock, on that part of the coast of Skye, an 

 intrusive sheet of dolerite, which is about 100 feet in thickness and 

 remarkably columnar in character, is seen forced between and cap- 

 ping a series of interesting Secondary rocks, the preservation of 

 which is clearly due to its presence and power of resisting denu- 

 dation. At points a little further to the south, on the coast of 

 Trotternish, as many as eight or nine intrusive sheets of dolerite 

 may be traced traversing the Mesozoic strata in parallel planes. 

 Occasionally, indeed, as is well seen near the north point of the 

 island of Eigg, the intrusive sheets are so numerous and so close 

 together that the included beds of Secondary rock become quite 

 insignificant and subordinate to the igneous masses which have been 

 thrust between and now enclose them. 



But the most striking example of the kind which we are able to 

 adduce is unquestionably that of the Shiant Isles, where fragments 

 of the Secondary strata are seen to be entangled between two intru- 

 sive sheets of truly stupendous proportions. The uppermost of these 

 is over 500 feet in thickness, and consists of excessively coarse dole- 

 rite passing into augitic gabbro, the whole having a grandly columnar 

 structure, the columns having a diameter of 5 or 6 feet. Of the lower 

 intrusive mass only the upper part is seen, and it does not exhibit the 

 columnar structure in any thing like perfection. It is impossible for 

 the geologist to look upon the grand cliff of the island of Garaveilan, 

 with its facade of columns resting on a base of altered shale and 

 sandstone and rising to a height of more than 50 feet — the whole 

 constituting an object far surpassing Staffa, if not in regularity and 

 grace, at all events in grandeur — without reflecting on the enormous 

 amount of dislocation and crumpling of the surrounding rock-masses 

 which must have been produced when this tremendous wedge of 

 igneous material was forced into their midst. The igneous masses of 

 the Shiant Isles were not improbably connected with a centre of vol- 

 canic activity in Tertiary times, of which every trace has been since 



