54 REPORT — 1842. 



Rocks of the Corstorphine Hills near Edinburgh ;" his object in so doing being to 

 urge geologists to distinguish well between appearances caused by mechanical action 

 and those resulting from structure- The existence of abraded surfaces of rocks in 

 these hills was (he stated) pointed out long ago by the celebrated Sir James Hall, 

 but when they were inspected by himself in 1840, in company with Mr. MacLaren 

 and Dr. Buckland, the surfaces which he then saw were marked by sets of wavy 

 parallel grooves or undulations (precisely similar to the casts sent formerly to the 

 Museum of the Geological Society of London), which appeared to him to belong to 

 a class of phasnomena distinct from the striated surfaces so common around Edin- 

 burgh and in many parts of Scotland. This opinion was confirmed by discovering in 

 the newly quarried body of the same rock of the Corstorphine Hills and at various 

 levels, undulations and grooves precisely similar to those on the surface, which were 

 thus shown to have been superinduced by original structure, an opinion which he 

 (Mr. M.) expressed upon the spot, and which he has published in his last Anniversary 

 Discourse. This view is indeed accepted by Mr. MacLaren, but that author at the 

 same time goes on to show, that on recent examination Sir G. Mackenzie and him- 

 self observed that the surface of parts of the Corstorphine Hills were also marked by 

 the small striae or irregular parallel scorings directed from west to east, and which 

 they believe must have resulted from powerful abrading agency, whether gravel and 

 water, glaciers or bottoms of icebergs. 



In thanking Mr. MacLaren for again calling attention to a subject he had so well 

 illustrated (see MacLaren's ' Sketch of the Glacial Theory'), the President said, that 

 he was quite ready to agree in all that had been written by that author in reference 

 to the Corstorphine Hills ; for although he had not seen the rough striae in his hurried 

 visit to that spot, he was well acquainted with such markings in many other parts of 

 Scotland, in which country, as well as in Sweden and Russia, he had endeavoured to 

 account for their presence by the grating action of the bottom of floating icebergs. It 

 was from this conviction (1840) that he opposed the terrestrial glacial theory of 

 Agassiz, as applied by that naturalist and Dr. Buckland to the low countries of Scot- 

 land, over which they contended that glaciers had advanced, which had scored all the 

 rocks, and which, on melting, had left moraines of gravel and sand. He was there- 

 fore happy to perceive, that in rendering justice to the merits of Sir J. Hall, Mr. 

 MacLaren had adopted the opinion for which he (Mr. Murchison) originally con- 

 tended; viz. that whilst icebergs very probably produced striated surfaces, the wavy 

 undulations are unequivocally due to the original structure of the rock*. 



On the Strati/led and Unstratified Volcanic Products of the West of England. 

 By the Rev. D. Williams, F.G.S. 



This communication was supplementary to that which Mr. Williams made last year 

 at Plymouth. Subsequent investigation, on a far more extended scale, had confirmed 

 him in the results he then announced, viz. that granite, gneiss, mica-schist, porphyry, 

 greenstone, tufaceous ash, breccia, grit, chloritic, talcose, and clay slate, were all vol- 

 canic products, and that no such distinction as the so-called " plutonic rocks" really 

 existed in nature — they were, in short, associated together by evidences of their com- 

 mon origin, and connected together by a series of mutual dependencies, and as such 

 were capable of definite classification, as erupted products, as rocks in situ, which 

 have been fused, semi-fused, or had been in some other particular stage of fusion. 

 and as rocks simply altered by contact with ejected burning lavas. His object was 

 to reduce the entire family of ancient volcanic products within the scope of recog- 

 nized laws, and the ordinary operations of nature. He pointed to a diagram he had 

 constructed, of an ideal volcanic centre in a phasis of activity, which (by admitting 

 modifications to a greater or less amount) he submitted might serve as an illustration 

 of the process of fusion and conversion (so far as the rocks of the earth had been 

 submitted to our view) throughout all regions and all times. He supposed an in- 

 ternal nucleus of white incandescent lava, whose outer border was surrounded by a 

 zone of gneiss, the zone of gneiss by an outer concentric zone of mica-schist, and the 

 mica-schist by any sedimentary strata, as the case might be; under certain circum- 



* Mr. Bowman has since (Phil. Mag. Nov. 1841) shown that some structural appearances 

 in the rocks of N. Wales might be mistaken for the result of glacial action. 



