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traps. 6th, Intrusive felspathic traps. By adopting a different 
colour for each of these classes, the general relations of an intricate 
trappean district could be shown at a glance. 
Although it was well known that the trap-rocks of Scotland 
belonged to several distinct geological epochs, much still remained 
to be done, both in determining their exact age and in working out 
the details of their structure. The author had been engaged in 
this subject for several years, and the present paper was intended as 
the first of a series elucidatory of Scottish trappean geology. 
Silurian . — It was remarked that, both in the Lower Silurian grits 
of the Lammermuirs, and in the Upper Silurian grits of the Pentlands, 
there is an abundance of felspathic matter, pointing to the existence 
of felspathic rocks, either then or previously ejected. The Lammer- 
muir chain is likewise traversed by innumerable felstone dykes, 
probably produced at the time of the folding of the Silurians. At 
Heston, in Berwickshire, beds of ash occur in the Lower Silurian. 
Old Red Sandstone . — The author referred to a previous paper 
(read before the Geological Society) in which he had shown that the 
Old Bed Sandstone of the south of Scotland consists of two distinct 
portions — one conformable with the Upper Silurian, and traversed 
by the same foldings and dykes ; the other lying utterly unconform- 
ably, both on the Upper Silurian and the Lower Old Bed. The 
igneous rocks of the older series probably occur in the Sidlaw Hills ; 
those of the newer series are well displayed in the Pentlands, the 
structure of which was detailed. 
Carboniferous . — The great abundance, the variety of character,, 
the local nature, and the great vertical range of the carboniferous 
traps of central Scotland, was shown by a detailed sketch of the 
geology of the Lothians. The range of hilly ground between Bath- 
gate and Linlithgow was pointed out as an eminently characteristic 
district. A careful survey had shown that no well-marked zone 
of the 6000 or 8000 feet of carboniferous strata in some part 
of the Lothians was without traces of contemporaneous igneous 
eruptions. 
Oolitic . — The structure of Skye and Baasay was described. These 
islands (when examined along a section from Dun Can, in Baasay, to 
Dunvegan, in Skye) consist of successive sheets of greenstone, with 
intercalated seams of estuary limestone, shell, sandstone, and coal, 
belonging to the Oolitic series. 
