240 Correspondence — Br. A. Irving. — Miscellaneous. 



C0E,ie-:Es:P03:sriDS3:srGE, 



DYNAMIC METAMORPHISM OF EOCKS. 



Sir, — Tt is from no mere love of controversy that I should like 

 just to say, in reply to Mr. Hatchings' query (Geol. Mag. for April, 

 1891, p. 168), that — while I am unable to appreciate unnecessarily 

 realistic play upon a metaphor which is no invention of mine, and 

 have no right to quarrel with him if he is still smitten with 

 the charms of the fallacy to which I referred — it seems to me that, 

 to apply the term " dynamic metamorphism " to a rock whose 

 internal structure shows no signs of differential movement (under 

 pressure) of its constituent pai'ticles, is only another instance, added 

 to those with which we are already too familiar in petrology, of the 

 abuse of technical language. Further, Mr. Hutchings seems to 

 me to surrender the point in the very next paragraph, if the Coal- 

 seams, by undergoing compression, have acted as buffers to relieve 

 the fire-clays of that portion of the mechanical force which otherwise 

 might be expended upon them to induce a cleavage-structure, in 

 those larger movements, to which the Coal-measures of Northumber- 

 land as a whole have been subjected. Thei'e seems to be some 

 confusion between dynamic agencies of change in the internal 

 morphology of a rock and what Prof. Judd has described as static 

 (Geol. Mag. 1889, Dec. HI. Vol. VI. pp. 243 et seq.), the potency of 

 of which I had previously recognized in my Thesis (see CJiem. and 

 Phys. Studies, etc., pp. 53-55, 93) to the extent of inducing such 

 metamorphic alteration in chemical compounds previously formed as 

 might complete their individuality qua minerals. 



This being so, I may be allowed to repeat my thanks to Mr. 

 Hutchings for his most valuable contributions of facts, the full 

 value and bearing of which will perhaps be better seen, when the 

 present acute stage shall have passed of that " pressure on the 

 brain," under which English petrology would seem at present to be 

 suffering. 

 Wellington College, Berks, A. Irving. 



4tth April, 1891. 



nynisozEiLXiJLn^iEiOTJS. 



Discovery of Lower Silurian Fishes. — At the meeting of the 

 Biological Society of Washington, on February 7th, 1891, Mr. 

 Chas. D. Walcott, of the United States Geological Survey, announced 

 the discovei'y of numerous dermal plates apparently of fishes in a 

 formation believed to be of Trenton age, near Cafion City, Colorado. 

 Mr. Walcott contemplates presenting a full account of the subject to 

 the Geological Society of America at their forthcoming meeting in 

 Washington in August next. 



