Correspondence — Mr. G. S. Klnahan. 191 



In answer to question 1, I would refer to Phil. Mag. 1874, page 

 205, also to pages 446, 467, Geol. Mag. Dec. II. Vol. II. 1875, for 

 my formulas of increase of velocity of water with increase of quantity 

 flowing, although slope is not altered. In answer to question 2, 

 the Pluvial period is described, page 105, Quart. Journ. vol. xxiv. 

 1868, Tylor, Amiens Gravel. In answer to question 3, Hopkins's 

 paper referred to is line 3, page 233, vol. viii. Cam. Phil. Trans. 

 In answer to question 4, 1 explained in my letter how I arrived at the 

 velocity being three times greater in the Pluvial period. But on page 

 63, vol. XXV. Quart. Journ. 1869, I give some cases in which the 

 water flowing must have been 129 times greater than at present. 

 At page 9, op. cit., I suggest a rainfall of 300 inches in the Pluvial 

 period. 



I would also recommend Mr. McJames to read Login on the Ganges 

 Valley, who refers to my papers in the Quart. Journ. Geol. Soc. 



With regard to a wet period, M. Belgrand, of Paris, in his great 

 work on the Gravels of the Seine, found, in 1871-2, that it was im- 

 possible to explain the size of the valleys and the deposits of gravel, 

 without assuming a wet period in which the rainfall was twenty or 

 twenty-five fold that at present in that part of France, thus confirm- 

 ing my view published in 1868. By the equation, page 467, Vol. II. 

 Dec. II. Geol. Mag. the velocity increases the cube root of the increase 

 of the quantity. If the rainfall was as stated by Belgrand and myself, 

 the velocity of streams should be three tiines as much as at present, 

 and the moving force would be as the sixth power. Then 3^^ =: 729, 

 that is to say, where a stone now of 1 lb. weight can be moved, a 

 stone of 729 lbs. weight could then have been lifted. In the Upper 

 Ganges, running through a great gravel formation, the water-level 

 never reaches now within 30 feet of the top of the banks. India 

 exhibits the proof of a former Pluvial period. 



London, March 11, 1882. A. Tylor. 



SUPPOSED LAUB.EXTIAN ROCKS. 



SiK, — When I received the March Number of the Gkol. Mag., I 

 learned that the Philistines were upon me ; but as I have so little 

 time to spare, that I cannot even read the papers, my letter must 

 necessarily be short. 



Dr. Callaway visited the Wexfoi'd district without my maps, and 

 left the most important sections unvisited, and that he does not 

 know my work is evident from what he has written about it. I 

 suggested he should visit West Galway ; because, in that country, 

 he would find the rocks so well exposed that his supposed uncon- 

 formability in the Wexford rocks southward of Greenore would be 

 then explained. I cannot understand where he obtained the obsolete 

 maps ; as, after my maps of the Wexford district were published, I 

 could not obtain copies of the old ones from any of the authorized 

 Irish publishers. 



To Professor Hull's letter it is unnecessary to make any reply. 

 GoEEG, March %th, 1882. G. H. KiNAHAN. 



