Mk. Bkyce 071 the Parallel Roads of Lochaher. 105 



present state of inqiiiiy, to admit many successive equable sinkings of the 

 waters of the ocean all over the globe, the same difficulties and hesitation 

 must be experienced in receiving Mr. Chambers' explanation as the true 

 theory of the Parallel Roads. Besides, the speciality of the phenomena is 

 by no means accounted for on this hypothesis. It appears to me to require 

 a special local cause. On the hypothesis of the shelves being formed by 

 the sea, it cannot, I think, be shown why other Highland glens were not 

 equally impressed ; or that any conservative influences have operated in 

 Lochaber, which were not just as likely to prevail in other places. This 

 argument cannot be properly estimated by one who has not seen the 

 shelves in Glen Hoy and Glen Gluoy ; from examining sea and lake- 

 terraees, from descriptions and drawings, the faintest conceptions only 

 can be formed of the wonderful reality. Any one on whose view the 

 scene which is presented on turning the flank of Bohuntine hill, bursts for 

 the first time, must look with the deepest astonishment at the distinctness, 

 continuity, and extent of the shelves ; he will feel how inadequate were 

 all his conceptions, and how little the Parallel Roads have in common 

 with any appearances which have come under his notice before. Mr. 

 Chambers eloquently describes the first impressions, and acknowledges 

 the " singular distinctness '' of the shelves in this locality ; yet his theory 

 afibrds no explanation of a phenomenon so remarkable. But this argu- 

 ment has been so ably handled by Mr. Milne in his reply to Mr. Darwin, 

 (Ed. N. Phil. Journ., vol. xliii. p. 437,) that it is unnecessary to insist 

 further upon it. 



The faint and higher markings on the south side of Glen Spean, which 

 Mr. Chambers lays so much stress upon as supporting his view, I did not 

 notice. " The whole," he says, " might appear doubtful to many persons; 

 in an unfavom-able light, a hasty observer might pass them by altogether 

 unnoticed.-' These may have been my circiuustances, and I do not 

 therefore question the existence of such markings ; but I cannot regard 

 the conclusion as warranted by the facts — the existence, namely, " in 

 Glen Spean of a body of water at levels above the bamers assigned to it 

 by M'CuIloch, Lauder, and Milne." Are not these and similar slight and 

 local markings best explained on the received theory — original inequalities, 

 the action of currents upon the submerged land, or occasional pauses in 

 the process of elevation ? 



While thus dissenting from the theoretical conclusions at which Mr. 

 Chambers has arrived, I cannot forbear to express my high admiration of 

 his patient and active research, — his clear, truthful, and eloquent descrip- 

 tions, — and of the service he has rendered to geology by his many exact 

 measurements, and by proposing a theory which will lead to a more care- 

 ful study of phenomena of this class. 



V. — Mr. James Thomson's Theory. 

 The lake tlieory has gained immensely of late by the advocacy of Mr. 

 David Milne. His paper, already referred to, is perhaps the most able 



