60 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 16 



about E. 40° N., differing 5° from the mean of the observations. He 

 also ascribes the upheaval of the Grampians to the same great con- 

 vulsion ; and it is remarkable that the narrow zone of clay-slate, ex- 

 tending from Stonehaven to Arran, has for the greater part of its 

 course a direction of E. 36° N., almost identical with the mean of the 

 observ^ations in the south. This band of slate may thus form the con- 

 tinuation of the Silurian beds on the south, rising up on the other side 

 of the synclinal valley in which the carboniferous strata of Scotland 

 have been deposited. The mineral character of the rocks is not op- 

 posed to this view ; and though no fossils are known in the northern 

 slates, yet in Glen Halmidel in Arran I found spheroidal bodies 

 similar to some veiy common in Peebles-shire, and which are pro- 

 bably organic, perhaps casts of a species of trilobite. 



The direction of these chains is thus not very different from that 

 which the theory would require. The elevation of this system is 

 placed by the distinguished author in the interval between the close 

 of the Silurian and the commencement of the old red sandstone de- 

 posits. The latter were formerly* shown to rest unconformably on 

 the edges of the upturned Silurian strata, and also to fill valleys ex- 

 cavated in them subsequent to their elevation. This would carry back 

 the formation of the chain to a period much anterior to the deposition 

 of the sandstone ; but as this rock in the south of Scotland should 

 perhaps be rather associated with the carboniferous than with the true 

 Devonian beds of England, an interval of sufficient duration for the 

 various changes, which the strata have evidently undergone before 

 they were covered up by the superior beds, may thus be obtained. 



But although the general direction of the strata and the period of 

 their formation do not differ much from that required, there are 

 other facts in the physical structure of this part of Scotland less fa- 

 vourable to this ingenious theory. The Pentland hills, which have 

 undoubtedly been formed subsequent to the deposition of the old red 

 sandstone, or rather of the coal-measures, have a direction of E. 40°N., 

 thus agreeing exactly with the line assigned to the Westmoreland 

 system. The same direction is reproduced in many of the ridges in 

 the coal-field of the Lothians, and also in the trap rocks of Fife and 

 the Ochils. In these instances we have parallelism of direction with- 

 out identity of age. On the other hand, the Cheviots on the south 

 probably coincide in age with the Pentlands, and also in their general 

 direction ; but the porphyry rocks constituting their eastern and 

 highest portion form ridges running N.N.E., and thus vary much 

 from the direction of the chain of which they form a chief part, and 

 also from the system of the North of England, with which they 

 should be closely related in time. The structure of this part of Scot- 

 land thus confirms the objections to this theory which Sir Henry de 

 la Beche long ago derived from the lines of elevation observed in the 

 south of Englandf . 



* Quart. Journ. Geol. Soc. vol. iv. p. 199. 



t Geol. Manual, 3rd edit. p. 489. M. E. de Beaumont indeed states that there 

 is a tendency in the older lines of elevation to influence the more recent elevations 

 in their vicinity. This, however, so far from removing the objection, admits its 

 tmth, arid consequently that parallelism in direction, even in neighbouring moun- 

 tain-chains, is no proof of identity in the time of their elevation. 



