Correspondence — A. R. Hunt. 479 



III. — Brief Notices. 

 Changes of Level in the Nile Valley. — In an article on 

 "Elevation and Depression in the Nile Valley" {Cairo Scientific 

 Journal, April, 1909), Dr. W. F. Hume summarizes the conclusions at 

 which he has arrived as follows : — 



1 . Elevation due to folding that resulted in fracture (not necessarily accompanied 

 by faulting), and gave rise to the A^'ile Valley cleft. 



2. Depression to at least 250 feet in late Pliocene times, admitting the sea up the 

 Nile Valley at least as far as Sidmant, determining a chain of lakes in the vaUey, 

 and the accumulation in them of thick deposits of raiu-eroded materials. 



3. Elevation to at least 600 feet, involving the drainage of the lakes, the cutting 

 back of the cataracts, and the deepening of the river valley. 



CoTTEswoLD Natukalists' Field Club. — The Proceedings, vol. xvi, 

 pt. iii, June, 1909, contains a short article " On the occurrence of 

 6'Affra-nucules in the Forest Marble of Taiiton, near Kemble, 

 Gloucestershire", by Mr. Charles Upton, who names the new species 

 Chara Icevigata. Mr. T. S. Ellis deals with the origin of " The Lower 

 Severn Valley, River, and Estuary from the "Warwickshire Avon to the 

 Bristol Avon", and combats the notion that the Lower Severn was cut 

 backwards so as to behead a stream which was formerly connected with 

 the river-system of the Thames. Mr. L. Itichardson contributes a 

 " Note on Pollicipes aalensis, Richardson" (described in the Geological 

 Magazine for August, 1908), and also a short article on " The Dorset 

 and Hampshire Coasts, with particular reference to the Forest Marble 

 Beds near Langton Herring ". 



coi^DRESiPonsriDEnsrcE. 



THE OLD AND NEW THEORIES OF IGNEOUS ROCKS. 



SiE, — Your review of Mr. JLarkev' s JVatural His fori/ of Igneous Rocks 

 inferentially gives judgment against my two 1903 papers in the 

 Geological Magazine on all points. So I crave a word of explanation. 



After General McMahon's reply, in November, 1903, to my 

 "Crystallization of Granite" appeared, I learned to my regret how 

 ill he was, and that the controversy had troubled him. I at once 

 wrote to express my regret, and received a most friendly answer. 

 There, so far as the Magazine is concerned, the matter dropped, 

 leaving me apparently crushed. 



I subsequently submitted my paper to two physicists and to 

 Dr. Sorby, with a view to clearing up outstanding doubts, if possible. 

 Dr. Sorby gave me a general permission to use his letters, and I got 

 all the leave I asked for from the physicists. I subsequently reviewed 

 the whole controversy in the Transactions of the Devonshii-e Association. 

 The dispute thus remains at a loose end, with no attempt by the 

 petrologists to settle it. 



To give you an idea how loo.se the ends are, I may say that in 

 October, 1903, a physicist wrote as follows: — "My best thanks for 

 the copy of your paper and letter accompanying it. I should not 

 wonder if the petrologists are all adrift." 



I see that your reviewer considers that the old doctrine of the 

 permeability of rocks by overhead waters has been finally disposed of. 

 Now geologists always rely on the explosive or expansive action 



