608 TRANSACTIONS OF SECTION C. ' 



of the Deccan Trap towards the end of Cretaceous times, and thereafter followed 

 the depression of the Gangetic belt with the folding up of the Himalayan range. 



As the Deccan Trap spread in thin sheets over large areas, it presumably 

 came out in a high degree .of lluidity and with a high temperature, while its 

 mass was too great for its eruption to be due to fusion by accidental local 

 causes. It is thus justifiable to assume, as the most probable of hypotheses, 

 that it represented the outwelling of the persistent, subcrustal, basic magma, 

 which is assumed by many on other grounds to exist in a state of fluidity, or 

 potential fluidity, at about 30 to 50 miles below the surface. 



It has been asserted that Dutton's theory of isostasy necessarily incurs a 

 perpetuation of the process of increasing depression in the area being loaded, 

 and of continued uprise in the adjacent area which is exposed to denudation. 

 Rut if my deduction as to the origin of the tension faults in Peninsular India 

 be justified, and if the Deccan Trap outburst was caused by the culmination of 

 this process, we have an instance which shows that isostasy can come to an end in 

 suicidal fashion, and thus a formidable objection to Dutton's theory is removed. 



By borrowing an idea ably expounded in a series of papers by Professor 

 R. A. Daly, of Massachusetts, we have also, with the facts briefly indicated 

 above, a reasonable explanation of the Gangetic depression and of the heavy 

 band which underlies the alluvium in a direction parallel to the tension faults 

 further south. Professor Daly assumes that under favourable circumstances the 

 sub-crustal gabbroid magma may enter the shell of tension, which has been 

 postulated by Mellard Reade. C. Davison, G. H. Duwin, 0. Fisher, and M. P. 

 Rudski to exist usually below the superficial shell of compression. He also shows, 

 from purely mechanical considerations, that intrusions into this shell tend to 

 expand into batholiths, and, by reducing the tension, tend to pull down the surface 

 into marked geosynelines. ' If now we assume that in the northern part of 

 Peninsular India the stresses during Palaeozoic and Mesozoic times were pre- 

 dominantly in a north-south direction, as indicated by three generations of 

 precretaceous, normal faults, we may likewise assume the production of basic 

 batholiths with a general east-west alignment in Northern India. These deep- 

 seated masses of basic (or probably ultra-basic) rock are suggested as the cause of 

 t'ne subterranean band of high gravity as well as of the Gangetic depression; 

 the withdrawal of the material forming the batholiths may account also for the 

 deficiency of gravity under the visible Himalaya as well as for some distance 

 southward under the plains along the foot of the range. A similar, though 

 possibly less pronounced, distribution of gravity should on this theory be found 

 along the Indus valley to the south-eastwards of the Baluchistan folds. 



2. Discussion on the Concealed Coalfield of Nottinghamshire, Derbyshire, 



and Yorkshire. 



(l) On the Concealed Portion of the York, Derby, and Nottingham Coalfield. 



By Professor Percy Fry Kendall, M.Sc., F^G.S. 



This great coalfield is a basin of which only the western moiety is exposed, 

 the other part being concealed by a discordant cover of Permian and later rocks. 

 Many attempts had been made to define the limits of the concealed extension, 

 but these were based upon no principle. When the author was invited to report 

 upon the question to the Royal Commission on Coal Supplies in 1905 his atten- 

 tion had already been directed to a possible solution of the problem by reference 

 to the remarkable attenuation of the Jurassic and Lower Cretaceous sequence in 

 the tract of country about Market Weighton. Here the rocks that, in the 

 Cleveland area and on the coast to the north of Flamboro' Head, attain a 

 thickness of upwards of 3,000 feet are reduced by failure of deposition or by 



1 See especially Professor Daly's paper ' Abyssal Igneous Injection as a 

 Causal Condition and as an Effect of Mountain-Building,' A/ner. Journ. Sci.. 

 xxii., 1906, 195-216. 



