536 EEPORT— 1882. 



-S"^ TURD A Y, A UG UST 2Q. 



The Section did not meet. 



MONDAY, AUGUST 28. 



The following Papers were read : — ■ 



1. Meniion of an example of an Earlij Stage of Metamorj)hic Change in Old 

 Bed Sandstone Cunglomerate, near Aherfoil. By Professor James Thom- 

 son, LL.D., F.B.S. 



The present commuuication relates to metamorphic clianges noticed in Old Eed 

 Sandstone Conglomerate near Aberfoil, in cuttings on the new branch railway from 

 Buclilyvie terminating at Aberfoil. 



The author had an opportunity of seeing this on the occasion of a recent visit 

 to the railway, through the invitation of ]\]r. Charles Forman, of Messrs. Formans 

 and McCall, engineers of the line. 31r. Forman pointed out various geological 

 features which were e.xposed to view in the cuttings for the railway. Among 

 these were waterworn conglomerate pebbles, which had undergone distortion and 

 partial crushing, obviously indicating that they must have been from some cause 

 reduced to a semi-plastic condition. 



The phenomena of these altered pebbles seemed to be of much interest in 

 connection with considerations or speculations as to what might be the softening- 

 agency to which they^ had been suljjected. Specimens were brought away ; and 

 some of them are now shown to the meeting. 



By inspection of tliese specimens it may be observed that they have yielded in 

 a plastic manner to the pressure of their contiguous neighbours, that they have 

 been impressed one into another at the spots of mutual contact, and that they have 

 bulged out and cracked open at interveningplaces between these spots of compression. 



The pebbles appear, many or most of them, to be quartzite. 



At various places in the cuttings of the railway within the first mile of its 

 course from Aberfoil, the Old Eed Sandstone Conglomerate of the district was found 

 to be altered in tliis way : but throughout the most of that space no such great 

 alteration was to be found, as the pebbles generally appeared not to have been 

 reduced to a plastic and yielding condition. 



Questions must now occur for consideration and research, which however 

 the author does not propose at present to answer, as to whether the softening 

 influence was merely a high temperatui-e producing a partial fusion of the stone ; 

 and, if so, how the heat came to be localized or applied at particular places more 

 than others ; also, whether hot water under great pressure, or hot gases, or vapours 

 of volcanic origin, were concerned in producing the eifects. 



The author presumes that such phenomena as those he has described must have 

 been already noticed in various localities ; but he thinks the subject may yet be 

 worthy of further research and consideration. From Mr. John Young, F.G.S., 

 Under-Keeper of the Ilunterian Museum in the University of Glasgow, he has 

 learned that Dr. Page, in a lecture delivered by him before the Geological Society 

 of Glasgow about 16 years ago, exhibited examples of similar quartzite pebbles 

 from the jSTethan Water, near Lesmahago, which were similarly cracked and dis- 

 torted by the pressure of contiguous pebbles. 



