Correspondence — The Rev. Dr. Irving. 575 



they occur in veins a quarter of an inch thick, or in masses many- 

 miles wide. 



Science is not advanced by the dreaming of dreams — to make 

 progress we require evidence culminating in proof. 



2 °' *™ \* VA ?X G. A. McMahon. 



10th November, 1890. 



PROF. PRESTWICH, F.R.S., ON THE ELEVATION OF THE WEALD. 



Sir, — I am much obliged to Prof. Prestwich for drawing attention 

 to an expression in my " Note on the Elevation of the Weald " 

 (Geol. Mag. September, 1890), to which I feel bound to say peccavi. 

 The fact is, when that paper was written, I was ignorant of the 

 view which the Professor had put forward so long ago as 1858 in 

 a paper, of which he has since been good enough to send me a copy. 

 When my 1883 paper was written, the only published statement 

 of Prof. Prestwich's view on the geological data of the Wealden 

 elevation, which I had before me, was that contained in the published 

 abstract of a paper read (in my hearing) before Section C of the 

 Brit. Assoc, at York in 1881. I am sorry I was misled by this; 

 and the more so as it was criticized by me more than once in the 

 1883 paper, to which the Professor refers. A copy of that paper 

 was sent to him at the time of its publication ; but, strange to say, 

 in the Professor's letter (which is now before me) acknowledging 

 the receipt of it (which seems to have been lost sight of since), and 

 offering some remarks upon some points in it, no notice was taken 

 of my criticisms on the York paper. Was it very extraordinary that 

 under such circumstances I was lulled into the belief that I had 

 correctly interpreted the statements contained therein? 



Prof. Prestwich will kindly allow me to refer to some remarks 

 I ventured to make in the discussions of Parts II. and III. of his 

 recent great paper, "On the Westleton and Mundesley Beds, etc.," 

 the substance of which is published in the Journal of the Geological 

 Society. These indicate, I think, sufficiently my position with regard 

 to this question. 



As to Mr. Clement Eeid's paper in "Nature" in 1886 (not 1888), 

 I did not feel the necessity of pointing out (what must be obvious 

 to any one who looks at it), that it was a "friendly corroboration" 

 of Prof. Prestwich's view expressed years before. 



The argument for contemporaneity, " on the ground of approximate 

 equality of altitude above the sea," I had no idea of saddling upon 

 Prof. Prestwich in particular. I mentioned it as the only argument 

 I had heard put forward by geologists, with whom I had discussed 

 the question, after I suggested in the pages of the Geol. Mag. 

 (1888) a different view to those generally held, from an examination 

 of the principal sections "in the field." 



As regards the " larger and more theoretical questions " raised in 

 my paper, I think I have sufficiently indicated the authorities which 

 have furnished the data from which my inferences are drawn. I am, 

 of course, allowed to draw my own conclusion from the Professor's 

 dignified refusal to consider them. 



