236 Transactions of the [Sess. 



may have examined. If we try to do so in the Pentland Hills 

 district, we are forced to the conclusion that a most complicated 

 series of phenomena have taken place between the Silurian period 

 and the present time. The first picture presented to us by the 

 study of these rocks is a comparatively quiet Silurian sea, teeming 

 with life, in which nearly every class of marine invertebrate fauna 

 was represented. Sponges, corals, star-fishes, crustaceans, and mol- 

 luscs swarmed in that Silurian sea. That this sea existed here for 

 a long period there is every evidence, from the immense deposits 

 of Silurian strata that can be seen in the largest patch exposed at 

 the head of the Nortli Esk and Lyne Water. Here we have an un- 

 broken series of Silurian strata upwards of 4000 feet in vertical 

 thickness, consisting of thin and thick bedded shales, sandstones, 

 and conglomerates, and occasional beds of limestone. They belong 

 to what is termed the Upper Silurian series. Above them in the 

 Lyne Water lie another set of beds, about 1000 feet thick, conform- 

 able with these Upi^er Silurians, which in all likelihood belong to 

 the lower portion of the Old Eed Sandstone system. These Upper 

 Silurian and lower Old Eed Sandstone beds, now standing in a 

 nearly vertical position, must have been deposited in a nearly hori- 

 zontal position in a gradually sinking sea-bottom, and often at a 

 very slow rate, as the nature of the beds and their fossil contents 

 show. But a sudden and extraordinary change came over this 

 long-standing and comparatively quiet sea of Silurian and Old Eed 

 Sandstone times in the neighbourhood of what is now the Pentland 

 Hills. This enormous thickness of strata was ruptured and turned 

 up on edge, sheets of molten lava were ejected through the uptilted 

 ends of the Silurian beds, while at the same time the waves at- 

 tacked these roclcs, breaking them up into fragments, rolling them 

 into pebbles, and piling up the materials in the hollows of the sea- 

 bottom. Neither did the materials ejected from the interior escape 

 the general denudation, for the sections now exposed show that the 

 volcanic matter was attacked and reduced to a paste which helped 

 to cement the pebbles and other fragments of rock which form the 

 conglomerates and sandstones contemporaneous with those out- 

 bursts. How long this battle between Vulcan and Neptune raged 

 we have no means at present of knowing, but it is evident that, 

 before the close of the Carboniferous period, Neptune had managed 

 to bury the works of his antagonist beneath several thousands 

 of feet of sedimentary strata ; for from a study of the geology of 

 Mid-Lothian, we are forced to the conclusion that the Carbonif- 

 erous rocks of the district lay in an unbroken sheet over where 

 the Pentland Hills now stand — at least, over the north-eastern por- 

 tion of these hills. But after all this deposition of Carboniferous 

 strata, amounting in all to possibly about 10,000 feet, another 

 convulsion, or other convulsions, shook the district, and all this 



