390 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 1 , 



call for a separate histoiian, who shall describe the nature, and, if 

 possible, fix the age, of all the successive coats of the older crystalline 

 rocks which are folded around that vast igneous nucleus, just as 

 Colonel Imrie did in reference to one transverse gorge, which he laid 

 open so admirably forty years ago. We have yet to ascertaiu the 

 exact relations of the uppermost clay- slate of Forfarshire to the 

 overlying Arbroath flagstone, which must be considered the base of 

 the Old Ked Sandstone of that tract. "With the expansion of the 

 older stratified crystalline rocks as they fold over to the S.E., it must 

 be borne in mind that there, are numerous centres of eruption, such 

 as that, for example, of Ben Cruachan, in Argyllshire, and other 

 mountains to the south and east of it, which penetrate and throw off 

 the stratified masses into various undulations. Other anticlinals 

 and synclinals occur without any such apparent motive cause, as in 

 the clear and unambiguous section of Loch Eck, in Argyllshire, to 

 which I formerly called attention*, and where a vast mass of gneissose 

 mica-schist is seen to rise from beneath the chloritic schists and lime- 

 stones of Loch Pyne. When the geological surveyors shall be pro- 

 vided with accurate maps, I trust that all these stratified masses of 

 the crystalline rocks of the Highlands will have their true relative 

 places assigned them. In the mean time much may be done, not 

 only in the endeavour to rival Mr. Peach in detecting fossils, but 

 also in the effort to coordinate the fractures which these stratified 

 masses have undergone, and to read off the periods when numerous 

 fissures were made, — the one set longitudinally, or along the strike 

 of the beds as seen in Loch Ness and the line of lakes of the Cale- 

 donian Canal — the other transverse, or across the strata, of which 

 the North-western Highlands offer many striking examples, to some 

 of which allusion has already been made. 



I cannot attempt to describe all the lithological variations in the 

 rocks which I believe to be the geological equivalents of the cry- 

 stalline rocks of the N.W. Highlands, in the counties of Aberdeen, 

 Banff, &c. From what I saw, however, in former years, of the thin 

 micaceous flag-stones and clay-slates, &c. of those tracts, I have 

 little doubt that they belong to the same series as that now under 

 consideration. The granitic mountain of Ben na Chie, which I then 

 examined, seemed to me to have performed precisely the same erupt- 

 ive part in the east as Ben Cruachan in the west, perforating stra- 

 tified sedimentary rocks, and producing much alteration in them 

 near the points of contact. 



The general view of the succession here offered must, however, be 

 alone tested by traversing the northernmost counties from N.W. to 

 S.E., and by marking the manner in which one gToup succeeds the 

 other. In such examinations, a great number of dislocations like 

 that which has been noticed in Suilven of Assynt, and numerous 

 anticlinals and synclinals, with outbursts of igneous rocks, will 

 doubtless be detected, by which, and by parallel upheavals, the 

 same set of beds will be found to have been frequently repeated 

 between the two coasts. 



* Quart. Journ. Geol. Soc. vol. vii. p. 169. 



