294 PROF. T. G. BONNET ON THE [May I9OO, 



tourmaline, rarely acicular in habit or blue in colour. Another 

 (same locality) is much more minute in structure, and the tourma- 

 line is still less characteristic, though here and there it can be 

 identified. A third (same locality) is mainly composed of this 

 exceedingly minute filmy mineral, of which one would be dubious, 

 did not small characteristic tourmaline-needles spread out from it 

 into a vein. Probably the rock was originally a mudstone. A fourth 

 specimen is banded, and may be described as combining the third 

 with the first : thoroughly characteristic tourmaline only appearing 

 in a vein. One or two other slices contain a trace of tourmaline, 

 but these four are my best specimens. 



In this connexion I may mention a specimen which is very like, 

 both macroscopically and under the microscope, to one of the light- 

 and dark-banded tourmaline-and-quartz rocks of the 'killas' in 

 Cornwall. Had it been given to me as coming from that district I 

 should have accepted it without question. This, however, was not 

 my only reason for collecting the specimen ; there was another, 

 namely, that I think it comes, not from the Bunter, but from the 

 Drift. It was a fairly angular block, at least 25 cubic inches in 

 volume, and it lay on a heap of stones near a woodman's cottage, at 

 the entrance of the copse called Huntington Gap ; that is, near to the 

 edge of the Driftless area of the Chase, and in one of the most lonely 

 parts, for, I think, there is no other cottage within a mile. Among the 

 trees erratics (Welsh and North Country) soon become fairly common.. 

 The specimen accordingly presents the following dilemma : — If from 

 the Bunter, how did it escape rounding? If from the Drift, where 

 was its home ? On the latter supposition, either rocks of Cornish 

 type must occur in Scotland or erratics sometimes came from the 

 south, as well as from the north and west, in the Ice Age. 



A small group of pebbles remains to be mentioned. These are 

 breccias. Certain of them seem to be only vein-quartz and not 

 worth minute study. Others show angular or subangular compact 

 fragments in a black matrix. I have examined three specimens. 

 In two, the fragments prove, as I expected, to be vein-quartz, 

 crushed probably by earth-movements : the matrix being composed 

 of smaller fragments of the same, cemented by secondary quartz and 

 tourmaline. The vein-quartz includes abundant cavities (rather 

 large in one specimen, smaller in the others), which contain bubbles. 

 From these the secondary quartz is usually free. The tourmaline 

 is both brown and blue, the latter as usual distinctly acicular, and 

 its needles occasionally appear to have inserted themselves for some 

 distance into the vein-quartz. The matrix of the second specimen 

 more nearly resembles a tourmalinized mudstone, as described above, 

 and has a slightly foliated aspect. In the third specimen the matrix 

 is mainly composed of minute granules of tourmaline, here and 

 there passing into clusters of prisms or needles of both tints. The 

 fragments are speckled with ferrite, and occasionally include grains 

 of quartz (one of which is pierced by the matrix) containing 

 numerous cavities with bubbles variable in size, and sometimes even 



