£96 PROF. T. Or. BONNEY ON THE [May I9OO, 



enough to transport the materials. I have estimated the Midland 

 Bunter — and am not aware that I have been convicted of exaggera- 

 tion — as a mass equal to a mountain-range 65 miles long, 4 miles 

 across its base, and 1 mile high, the pebbles alone representing a 

 similar range 20 miles long, 2 miles broad, and fully 1000 feet high. 

 As this requirement is irreconcilable with some hypotheses, I am 

 surprised that it has not been disproved, or at least disputed, by 

 those who have advanced them. 



IV. Possible Sotjeces of the Pebbles. 



(1) North Wales. — The Principality might contribute sand 

 enough, if the Old Eed Sandstone were heavily taxed ; but it has 

 neither the quartzites nor the quartz-felspar grits, nor the right 

 felstones, at any rate in quantities worth a moment's consideration ; 

 nor can it ever have supplied them, because, as the region is com- 

 posed of rock older than the Trias, they should still be visible at the 

 surface. 



(2) The Longmynds. — In the Midland region the only rocks 

 resembling the ordinary Torridon Sandstones occur in the Long- 

 mynds, where they are exposed over a considerable area, especially 

 in the north-western part. Here I examined them in 1896, with 

 my friend the Rev. E. Hill, and under the kind guidance of Prof. 

 Lapworth. As these rocks have a very important bearing on the 

 question before us I shall give some description of them, without, 

 however, touching the controversies which exist in regard to their 

 exact age and classification. The conglomerates and grits appa- 

 rently overlie, iu the district around Lyds Hole, a volcanic group, 

 consisting chiefly of compact rhyolitic lavas, sometimes with 4 pyro- 

 merides,' and presenting a general resemblance to those in the 

 Wrekin district, for which the name Uriconian has been proposed. 

 At the base of the ' Torridonians ' are grits, seemingly felspathic, 

 which are succeeded by a rather thick conglomerate (No. 1) com- 

 posed of beds of pebbles parted by seams of grit, the latter not 

 usually exceeding 2 feet in thickness. The pebbles (which, as far 

 as I remember, are often about the size of a hen's egg) consist 

 of vein-quartz, quartzite (not very abundant), old rhyolites (not 

 rare), and a granitic rock, the matrix being apparently an irregular- 

 sized quartz-felspar grit, sometimes curiously like the Torridon 

 Sandstone. This is followed by a thick mass of rather friable 

 purplish sandstone (probably tinted in parts by manganese), above 

 which is another conglomerate (No. 2) with fewer sand-partings, but 

 less strong than the lower one. It is thickly studded with sub- 

 rotund pebbles, occasionally 4 or 5 inches in diameter, but more 

 often from 2 to 3 inches, consisting of vein-quartz, quartzite, whitish 

 to reddish or purplish, having as a rule a rather satin-like aspect on 

 broken surfaces, and of streaky rhyolites. It is sometimes inter- 

 rupted by seams of a rather ashy-looking grit. This is succeeded 

 by a large series of grits, apparently more or less felspathic, which 





