430 Correspondence — Mr. G. Roper — Rev. 0. Fisher. 

 coiaiaEsiPOisrnDsisroE. 



THE STJPPOSED DICYNODONT FROM THE ELGIN TRIAS. 

 Sir, — At the meeting of the British Association at Aberdeen in 

 1885, much interest was excited by the alleged discovery of Dicynodon 

 in the Triassic sandstones of Elgin. Prefessor Judd stated his 

 belief in the specimen at the time ("Nature," Oct. 15, 1885, p. 573), 

 and said that the specimen was in the hands of Dr. Traquair. In 

 Woodward and Sherborn's "Catalogue" (1890) I notice these 

 authorities place a (?) before the reference, thus indicating the 

 doubtful nature of the find, while Lydekker in vol. ii. "Manual 

 of Palaeontology " does not even refer to it. Are we to interpret 

 Dr. Traquair's six years' silence as a withdrawal of the original 

 determination ? When an important discovery has been announced, 

 it seems only just that the geological public should hear more about 

 it, and this practice of throwing out vague and unsatisfactory state- 

 ments is very annoying to those who prefer exact information and 

 rather disparaging to the discoverer, who naturally expects so 

 great a find to be worthy of notice. G. Eopek. 



ON DTNAMO-METAMORPHISM. 



Sir, — I think Dr. Irving has not quite understood the reasoning 

 in my short article on Dynamo-metamorphism of a year ago. I 

 wrote, that the part of the work of compression expressed by the 

 product {P— W) w, where P is the compressing force upon a cubic 

 element of the disturbed mass, W the weight of the cover, and lo 

 the height through which the cover has been lifted, was emploj'ed 

 in bending and breaking the rock and overcoming friction, and that, 

 since this part of the energy is not reconvertible into mechanical 

 work, it must take the forms of heat and chemical action. He thinks 

 this " last term is surely outside the others altogether " ; that is, I 

 suppose, is employed upon the rock external to the portion of it 

 under consideration. But the expression is not very clear, though 

 his illustration in the note (p. 300) seems to show that such is his 

 meaning. He says there that, if a horse or engine draws a series of 

 loaded trucks along a perfectly horizontal line of rails, " work is done 

 in overcoming the friction of the wheels against their axles and against 

 the rails, and in the displacement of a portion of the atmosphere 

 with the movement of the train ; but would any one contend that 

 energy was stored up in the train ? " 



Energy of motion is so obviously stored up in the train that Dr. 

 Irving cannot refer to that. He must refer to the energy imparted 

 to the atmosphere, and to the energy absorbed by friction, which 

 last is distributed between the trucks and the rails. The energy 

 communicated to the air is " outside " the other effects, and so is the 

 energy absorbed by the rails. But the energy absorbed by the 

 friction of the wheels against their axles is partly converted into 

 heat, and is partly employed in producing a molecular change in the 

 iron, rendering it more granular and liable to fracture. I should 

 consider this a case of dynamo-metamorphism. Still it appears to 



