T. Mellard Reade — Normal Faulting. 487 



The third paper I wish to speak of is by Miss Eaisin, " On the 

 Lower Limit of the Cambrian Series in N.W. Cai'narvonsliii-e." 

 This I have only here to refer to as it deals with supposed Pre- 

 Cambrian rocks. One general observation is necessary. The 

 authoress continually speaks of my conclusions as " new." They 

 are in fact essentially the conclusions of Sir A. Ramsay, and the 

 only novelty about them is the reconciliation of these with some 

 portion of the more recent conclusions of other writers. 



The pi'oofs which I gave of the general correctness of Sir A. 

 Ramsay's conclusion Miss Raisin has sought to invalidate, and in 

 one case I have now to acknowledge she has done so with success. 

 On re-visiting Bryn-Efail I find that her reading of the section is 

 the true one, and my own is erroneous. I would make this acknow- 

 ledgment in any case, but I do it now with all the more readiness, 

 that I find that the mistake is an entirely gratuitous one. If my 

 reading had been correct, it would have constituted a difficulty, rather 

 than an aid in the true reading of the district. 



The fact is, that when I wrote my paper I was studying Pre- 

 cambrian rocks, and as soon as I found that there were none in the 

 district — for the proof of which the other observations are amply 

 sufficient, and had led me to this conclusion before ever I saw 

 Bryn-Efail — I grudged any more time for the subject, and was glad 

 of a short cut, which has proved to be disastrous. I saw that to 

 understand the real history of these volcanic masses involved a 

 survey of the whole of the Cambrian rocks of the district — a task 

 from which I shrank. That survey I have, however, now made, 

 and hope shortly to present the results. By this I have learnt, that 

 a great number of previous supposed results, some of my own among 

 them, are entirely wide of the mark. The only thing that becomes 

 clearer than ever is that there are no stratified Precambrian rocks in 

 the ordinary sense in North- West Carnarvonshire. These results will 

 render it useless to reply to any other points in Miss Raisin's paper. 



III. — A Miniature Illustration of Normal Faulting. 

 By T. Mellard Reade, C.E., F.G.S. 



WHEN examining the Glacial drift at Nevin, Carnarvonshire, I 

 observed in a banded silty clay occupying the top of the cliff 

 of drift at a point between Porth Nevin and Porth Bodeilias, an 

 excellent illustration of my theory of Normal Faulting.* 



The bed in question consisted of an extremely finely laminated 

 silty clay, sometimes called book-leaf clay, the laminations being 

 grouped in ribands about half an inch wide and six inches apart, 

 of lighter and darker colours, presenting a striped appearance very 

 conspicuous from the shore. In the upper part of the bed the bands 

 were continuous, though a little wavy : the lower part of the bed, 

 as far as it was visible above the talus of sand, was faulted as 

 shown in the accompanying diagram (Fig. 1). These faults simu- 

 lated in a remarkable manner sections of faulted coal-fields which 

 ^ Chap. viii. Origia of Mountaia Ranges. 



