TRANSACTIONS OF THE SECTIONS. 93 



On the Changes affecting the Southern Extension of the Lowest Carboniferous 

 Bochs. Brj G. A. Lebottr, F.G.S. 



In Scotland the lowest division of the Carboniferous series consists of the rocks 

 called "the Calciferous Sandstones" by Maclaren, and usually known in the 

 north of England as " Tuedian." Prof. Geilde has shown that the lower limit of 

 these rocks merges insensibly into the upper portion of the Old Red Sandstone series. 

 In England their upper limit seems to be equally indefinite, and runs in a kind of 

 lateraf dovetailing into the lower beds of the Carboniferous Limestone series or 

 " Bernician." It is this merging of Tuedian into Bernician which forms the subject 

 of the paper. Some remarks as to the terminology of the series followed, and also 

 a short account of the higher divisions of the Carboniferous as represented in the 

 north of England, pointing out especially that the mode of deposition there was 

 nearly of the same character from the base of the Millstone Grit to the Old Red 

 series, a slight and very gradual change from brackish to purely marine conditions 

 beino' the only one of a sufficiently marked and important character to be taken 

 into account. The author admits but two Carboniferous divisions — the Upper, con- 

 sisting of Coal-measures, G annister beds, and Millstone-grit; andthe Lower, inclu- 

 ding the Bernician or Carboniferous Limestone and the Tuedian or Calciferous 

 Sandstones. 



On the Parallel Roads of Glen Roy. By J. Macpadzean. 



On the Parallel Roads of Glen Roy. By Da\id Milne-Home, LL.D. 



The object of the author in this paper was to notice the views of Dr. Tyndall 

 given in a Lectm-e on Glen Roy, delivered in the Royal Institution, London, on 

 21st June, 1876. 



The author thought that Dr. Tyndall had allowed to himself too short a time, 

 viz. only two days, for an examination of the Lochaber district, as in that space it 

 was impossible to see more than a tenth part of the things which should be exa- 

 mined for a solution of the Parallel Roads problem. 



Dr. Tjndall had apparently gone to the district with preconceived opinions in 

 favour of the glacier theory to explain how the lakes had been confined. His know- 

 ledge of the Swiss glaciers eminently qualified him to see on the spot whatever 

 could be urged in support of that view. But, after all, the residt of Dr. Tyndall's 

 inspection had only satisfied him that there was a " probability " of the correctness 

 of the glacier theory, though a probability so great as in Dr. Tyndall's opinion to 

 " amount to a practical demonstration of its truth." 



To pave the way for the adoption of the glacier theory of lake-barriers, Dr. Tyn- 

 dall began his lectm-e by attempting to annihilate what seemed to him the only 

 other explanation worthy of notice, viz. that first suggested by Sir Thos. Dick Lauder, 

 and defended by Mr. Milne-Home, that the lakes were dammed by detrital blockage. 

 He states that this explanation may with safety be "dismissed as incompetent 

 to account for the present condition of Glens Gluoy and Roy." 



Dr. Tyndall, however, seems to have supposed that no better support could be 

 given to the detrital theory except what was stated in Sir Thomas Lauder's paper, 

 published about sixty years ago, ignoring altogether what had been advanced in 

 support of the theory by later writes. He, for example, states that the detrital 

 barriers were supposed by Sir Thomas Lauder to have been heaped up by " some 

 unknown convidsion," a view which no one now suggests, and which Sir Thomas 

 himself never entertained. 



What is stated in support of the detrital theory is, that a blockage existed at the 

 mouths of the glens, created by the detritus, which then filled the vftlleys, and 

 ■\\ hich reached even to tlie mountain tops at heights of nearly 2500 feet above the 

 sea. Dr. Tyndall admits the abundance of detritus at these heights, and even allows 

 that the Parallel Roads were formed on the detritus. 



Glen Collarig sliows that the baiTier there must have been only 700 or 800 yards 



