236 Correspondence — Prof. T. G. Bonney. 



idea of inserting a protecting clause did indeed occur to my mind, 

 but I abstained from so doing, because I supposed that I should be 

 credited with the possession of what is common knowledge. Readers 

 get wearied if, in writing geological papers, we imitate the style of 

 legal documents. I dwelt upon the thickness of the Staffordshire 

 pebble beds (which I understated rather than overstated), because the 

 strength of a chain is the strength of its weakest link, and I cannot 

 explain, for reasons already given, these conglomerates, as they occur 

 over a considerable area of the Midlands, by Mr. Mellard Reade's 

 hypothesis. The comparative absence of pebbles in the northern 

 region is undoubtedly an anomaly for which we have not yet found 

 the explanation (I could offer one, but, as it would be an hypothesis, 

 I abstain on the present occasion, lest I should trespass too much on 

 the Editor's tolerance). But on the hypothesis of a southern deriva- 

 tion, the much greater thickness which the Bunter group as a whole 

 attains in the district about the Mersey compared with that in Staf- 

 fordshire (more than double) is also an anomaly. To this I believe 

 we might add — though here, as my personal observations are not veiy 

 numerous, I must speak with caution — the greater abundance of 

 felspar fragments in the sandstones of the Lancashire-Cheshire 

 Bunter. So in this matter, as it appears to me, our difficulties are 

 mutually destructive, like Kilkenny cats, and they may leave us 

 much as they found us. 



But I cannot understand how the nature of the sand in the Bunter 

 helps Mr. Mellard Reade. " An inspection of the geological map of 

 Scotland shows such a diversity of rock structure, and there exist 

 such lithological differences in the various areas that would have 

 drained into these two hypothetical rivers, as to seem irreconcilable 

 with the required travel of sand southwards." This inspection, as it 

 seems to me, shows that the area chiefly drained would be the great 

 crystalline region — then doubtless more Alpine in character than 

 now, the fragments of which are called the Scotch Highlands. 

 Mr. Mellard Reade forgets that the detrital beds of this region 

 (which were doubtless also undergoing denudation at this epoch) 

 present no small resemblance to the Bunter Beds of England. 

 Parallels to this argument may be found in the sandstones of the 

 Carboniferous system in England, and in not a few cases in other 

 lands. 



(2) Mr. Mellard Reade falls into a second, though perhaps more 

 natural, misconception in regard to my views as to the efficacy of 

 tidal cm-rents. My doubts as to their potency referred to their action 

 under the physical conditions of the English Trias; that is, in an 

 elongated gulf (adopting for a moment his hypothesis), to which, 

 moreover, in all probability, the entrance was narrow and shallow. 

 To discuss the whole question would extend this letter too much, but 

 I must remark that citations concerning the action of the tide off the 

 British Isles, where the physical conditions are very dissimilar, do not 

 appear to me germane to the subject. 



Next, as to the defect. Mr. Mellard Reade refrains from noticing 

 my comparison of the Bunter of England to the Nagelflue and 



