140 Mr Buchanan's DeacnptioH and Uses of Prviracting Table. 



■ Apologizing, therefore, for having detained you long, and for having 

 previously too much extended a similar mode of reasoning, I take leave 

 of the glacial theory in congratulating American science in having pos- 

 sessed the original author of the best glacial theory, though his name had 

 escaped notice ; and in recommending to you the terse argument of Peter 

 Dobson, a previous acquaintance with which might have saved volumes 

 of disputation on both sides of the Atlantic. 



In the mean time, however, we may account for the transport of bould- 

 ers, the striation and polish of rocks, and the accumulation of superficial 

 detritus, we cannot quit the glacial subject without avowing our obliga- 

 tions to Venetz, Charpentier, and Agassiz, and above all to the last, for 

 having brought the agency of ice more directly into consideration as a 

 vera causa, to explain many phenomena on the surface. Even we who 

 differ from Agassiz in his generalizations, and have not examined the Alps 

 since the theory was propounded, should not hastily adopt opinions which 

 may be modified after a study of the glaciers in situ. ' " Come and sec" 

 is the bold challenge of the Professor of Neuchatel to all who oppose hira, 

 and sanguine as to the correctness of his opinions, he is certain that many 

 will be converted if they would but observe the phenomena on Avhich his 

 views are based. Truly we must acknowledge, that he was the first per- 

 son who roused our attention to the effects produced b}'^ the bottom of an 

 advancing glacier, and if geologists should eventually be led to believe, 

 that certain parallel scratches and stria' on the rocks were in some in- 

 stances due to glaciers moving overland, but in many other cases were 

 produced by icebergs, we must remember that the fertile mind of Agassiz 

 has afforded us the chief means of experimental!}' solving the problem. 



Description and Uses of his Protracting Table. By George 

 Buchanan, Esq., F.R.S.E., F.R.S.S.A., Civil Engineer, 

 Edinburgh, with a Plate. Communicated by the Royal 

 Scottish Society of Arts.* 



This instrument w^as formerly exhibited in the year 1827, 

 and was then honoured with the approbation of the Society 

 of Arts, and a medal awarded. Since that time it has been in 

 constant use, and I have found it of the greatest service in 

 numerous and extensive surveys which have been laid down 

 by it. Having been lately requested by Mr Buddie, the dis- 

 tinguished mining engineer in Newcastle, to superintend the 



Read before the Royal Scottish Society of Arts, 14th March 1842. 



