1 66 Notes on the Geological History of [Sess. 



gas, or poison, or a sudden access of salinity in the water ? 

 Did the water suddenly retire, leaving them to perish on the 

 sand ? Buchanan's observations in the summer of 1911, 

 described in the pages of ' Nature ' in December of that year, 

 when he found that carp, perch, tench, and pike buried them- 

 selves protectively in the mud on the approach of desiccation 

 due to an exceptional summer's drought, seem to present an 

 adequate explanation ; the fish, following a primitive instinct, 

 had buried themselves to avert the disaster of a temporary 

 drying-up of the lake, and their supply of oxygen gave out ere 

 the water returned. It imposes some strain on the imagina- 

 tion to realise that Blackford Hill, with its whinny slopes, 

 grassy hollows, and rocky view-points, with its twentieth- 

 century murmur, could be the stage of such a scene, and that 

 Holoptychius nobilissimus glided through the silent waters of 

 that remote age over rocks which are a happy hunting-ground 

 of the children of Edinburgh. 



Scotland derives her mineral wealth mainly from the 

 succeeding Carboniferous age, and for the intrepid naturalist 

 the Carboniferous, with its comparatively unbroken record, 

 provides an unexampled field for research. But the Old Bed 

 Sandstone, with its masterful tectonic problems, its unique 

 plutonic and volcanic complexes, its prodigious conglomerate 

 deposits, and its enigmatic palaeontology in the crises of 

 evolution, is for geological genius of the most consummate 

 order. One cannot think of the wellnigh impossible condi- 

 tions of existence of those times, compared with our teeming 

 superabundant world which has come from those times, with- 

 out a sense of veneration and amazement. 



Long before the close of the Upper Old Bed Sandstone age 

 the Blackford Hill of that time was completely buried by the 

 lake sediments, as is abundantly proved by the position of 

 rocks of that age at Liberton, Craigmillar, Grange, and Craig- 

 lockhart railway cutting. 



Following on this submerged area came the immense 

 deposits of the Carboniferous. Very early the Old Eed rocks 

 of the Pentlands were obliterated. From beyond Carlops to 

 far beyond the Forth shallow lakes, dismal swamps, lagoons, 

 open seas, and spasmodic bursts of volcanic activity spread 

 over the region some ten thousand feet of strata, sandstones, 



