PROCEEDINGS 
OF THE 
ROYAL SOCIETY OF EDINBURGH. 
vol. viii. 1873-74. No. 89. 
Ninety-First Session. 
Monday, 2d March 1874. 
Sir WILLIAM THOMSON, President, in the Chair. 
The following Communications were read : — 
1. On the Parallel Roads of Glen Roy. By the 
Rev. Thomas Brown, F.R.S.E. 
( Abstract .) 
After describing the general appearance of these terraces, the 
author referred to the discussions which had taken place as to 
their formation. More than fifty years ago it was conclusively 
proved by Dr Macculloch* and Sir Thomas Dick Lauder, f that 
these parallel roads are the margins of ancient lakes, and since 
then the question has been whether these were freshwater or sea 
lochs. Mr Darwin, Dr Robert Chambers, Professor Nichol, and 
others, have contended that they were marine ; while Agassiz, Dr 
Milne Home, Mr Jamieson, and others, have maintained that they 
were freshwater. 
As the problem is confessedly one of some difficulty, it seemed 
desirable to obtain, if possible, the evidence of fossils. It has been 
ascertained, indeed, that the deposits contain no shells nor similar 
remains, and Mr Darwin has suggested that they may have been 
destroyed by the carbonic acid gas absorbed by the rain-water which 
for ages has percolated through the beds. This, however, could not 
have taken place with the valves of diatoms, which are siliceous, and 
* Geol. Trans , ser. 1, vol. iv. f -Edin. Roy. Soc. Trans., vol. ix. 
2 X 
VOL. VIII. 
