116 Major- Gen. MeMahon — Culm-measures at Bude, Cornwall. 



beds were ground down to a powder before tbey were re-con- 

 solidated into crystalline scbists ? The crushing of rocks to powder 

 must surely have been a local phenomenon very limited in its extent. 



One hears much of Spring's experiments, but I have seen no 

 reference to those of Hallock, 1 who subjected layers of antimony, 

 beeswax, parafine, gi'ound bismuth, a second layer of parafine and 

 lead, with silver pieces stuck on the wax and parafine, to the pressure 

 of 6000 atmospheres. The materials came out unchanged, unmelted 

 and unmixed. The silver coins left their marks on the steel sides of 

 the instrument employed, but they did not sink through the wax 

 or parafine, which they would have done had the wax or parafine 

 liquefied. Mr. Hallock drew the conclusion from his experiments 

 that " to me they seem to establish that pressure alone cannot truly 

 liquefy a solid, i.e. diminish its rigidity, consequently we should 

 scarcely expect chemical or mineralogical changes to be produced 

 by pressure alone." 



In the Bude rock we have laid bare for our study, not a laboratory 

 experiment made under artificial conditions, but the operations of 

 Nature herself. The rocks are contorted, crushed, ruptured, and 

 compressed ; they have undoubtedly been subjected to very great 

 pressure ; how is it that they are not metamorphosed if pressure 

 alone is competent to produce metamorphism ? It cannot be said 

 that they have not been subjected to enormous pressure. It cannot 

 be said that they have not been sufficiently mellowed by the lapse 

 of those " countless ages with which geology deals," for the dis- 

 turbances that crumpled the Culm-measures would seem to have 

 been of considerably greater antiquity than those that gave birth 

 to the Himalayas. How are we to estimate the intensity of a squeeze 

 except by the crushing and crumpling produced by the squeeze ? 

 To say that the rocks would have been metamorphosed had the 

 squeeze been sufficient in intensity and duration is to beg the whole 

 question. 



That metamorphic rocks are often highly contorted rocks may be 

 freely admitted, but it does not follow from this fact that pressure 

 and metamorphism are related to each other as cause and effect. 

 Indeed, though contortion and metamorphism are sometimes found 

 to coexist in the same rocks, they are sometimes found apart. The 

 Bude rocks show that highly contorted rocks are sometimes devoid 

 of metamorphism, and I can point to the converse case where highly 

 metamorphosed rocks are devoid of contortion. I can point to a 

 considerable area in the N.W. Himalayas in which metamorphism 

 is at its maximum, but where the beds give little or no evidence of 

 disturbance. 



In my first paper on Himalayan Geology I desci'ibed my passage 

 over the Bupin 3 and some other passes. The beds traversed were 

 mica schists, siliceous schists, and gneiss. For a distance of 40 

 miles, measured in straight lines on the map, and up and down 

 over strata exceeding 10,000 feet in thickness, the ever-recurring 



1 American Journal of Science, 1887, p. 277. 



2 Elevation 15,480 feet. 



