1857.] GEIKIE SKYE. 3 



I. Character and sequence of the Liassic beds of Strath. 



It is a somewhat remarkable fact that in Scotland the Lias invari- 

 ably rests on a palaeozoic or metamorphic base — usually Old Red 

 Sandstone. And it is equally striking that the formation is confined 

 to the northern counties, among the hypogene and older palaeozoic 

 districts ; none being found to the south of the great granitic barrier. 

 These facts are of importance in investigating the physical history 

 of the country. The lias of Skye rests sometimes conformably and 

 often unconformably upon red sandstone or purplish-grey quartz- 

 rock. These underlying beds have never yet yielded any organic 

 remains, so that it is uncertain whether they should be regarded as 

 Old Red, Silurian, or some of the later portions of the gneissic series 

 of central Scotland. They graduate southwards, according to Mac- 

 culloch, into a series of gneiss- and mica-schists ; but considerable 

 doubt rests upon their stratigraphical relations, and it does not seem 

 probable that the difficulty can be cleared away without a careful 

 and somewhat extended examination, not merely of the rocks in 

 Skye, but of their prolongations into the mainland*. 



The boundary-line of the lias and red sandstone commences on 

 the north-eastern shore at the village of Lussay, whence it proceeds 

 in a south-westerly direction for three miles to a point about half 

 a mile south of the village of Sculamus, from which it runs nearly 

 due south to the hamlets of Heast on Loch Eishort. See Map, PI. I. 

 fig. 1 . This is a well-marked line ; for the observer may not un- 

 frequently stand at the same moment upon lias and red sandstone. 

 The only part on which there hangs a shade of uncertainty is at the 

 turning of the beds near Sculamus, where, owing to the thick cover- 

 ing of peat and the swampy nature of the ground, the two rocks 

 cannot be approximated quite so closely as along other parts of the 

 line. Yet this and similar obscurities could be shown only on a map 

 of a very large scale. 



I have been not a little surprised by the manner in which this 

 line is mapped and described by Dr. Macculloch. He commences 

 it at the head of the long narrow creek of Obe Breakish, instead of 

 at. the village of Lussay, thus colouring as red sandstone a space of 

 fully two miles in length, which is actually lias. After quitting 

 the shore his line is undefined, the formations being shaded into 

 each other, indicative of a very uncertain boundary. Beyond this 

 a large mass of syenite is introduced, breaking through the line, 

 and for about three miles separating the two rocks. They are re- 

 presented as meeting again to the south of the syenite, whence they 

 run south-west to the shore of Loch Eishort, near the farm of 

 Borereg — an error of considerably more than a mile. His lines are 

 thus frequently set down at random, great tracts of red sandstone 

 are altogether omitted both in map and memoir, the existence of 

 faults is ignored, long tracts of syenite are inserted where none exist 



* Since this paper was written, Professor Nicol's Memoir " On the Red Sand- 

 stone, Quartzite, &c. of N.W. Scotland" has appeared in the Quart. Journ. Geol. 

 Soc. vol. xiii. p. 17. 



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