2 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



produced by pressure of great earth-raovements, followed by mineral 

 changes, that I note a tendency to revert in some respect to the for- 

 mer position, or rather to affirm that, while admitting the existence of 

 great masses of gneiss and schist of indubitably Archaean age, these 

 may be so interfelted and interfolded with those of later date, so 

 crushed and modified subsequently, that it is impossible to go back 

 beyond the date of the last great mutation which, like a desolating 

 flood sweeping over a land, has effaced the traces of an earlier crys- 

 tallization or an earlier stratification. 



In consequence of this recognition of the effects of pressures due 

 to great earth-movements, it would be found, I think, very con- 

 venient to apply the term '■''pressure metamorpJiism^^ to cases where 

 the eff'ects of pressure may be recognized with reasonable certainty, 

 'and to reserve the term " regional metamorj^hism" for those ancient 

 rocks, occupying extensive areas of the earth's surface, which, 

 whatever be their history, are in all probability by no means 

 in their original condition. 



In the study of these questions my views have changed. I believed 

 and taught for years, as most geologists of my age would naturally do, 

 that gneisses and schists were in many cases metamorphosed Palaso- 

 zoic, if not later rocks. Gradually this faith broke down, not, 

 however, until it had led me into serious blunders*. Then, by 

 degrees, I began to recognize how much greater than I had hitherto 

 supposed were the results of pressure, producing crushing in situ, 

 often a rude cleavage, followed by some mineral change. Through 

 not knowing this, I had attributed too much weight to appearances 

 of a fragmental structure in gneissoid rocks, and had inclined to 

 refer some schistose crypto-crystalline rocks to altered tuff's, as 

 in the Sharpley and Peldar Tor rocks of Charnwood, instead of to 

 rhyolitic lavas, crushed in situ. My work in South Devon in 1883 

 opened my eyes a little to the effects of pressure as modifying rock- 

 structures ; but unluckily my work in the Alps a few weeks later 

 tended rather to throw me off the scent. The following year, how- 

 ever, convinced me how completely stratification could be simulated 

 by the results of crushing, and prepared me to accept, at any rate 

 in part, the statements of Prof. Lapworth as regards the " newer 

 gneiss " of Scotland, and of Dr. Lehmann as regards the Saxon granu- 

 lites. Yet, while listening to all who seemed to reason fairly and 

 seek to learn of nature, I have striven to follow no teacher, not 

 even myself, blindly, but to work at these questions, as is right, 

 in the spirit of a sceptic, who, however, believes that truth can be 

 found sooner or later. 



Let me say now, once for all, that I make no claim to originality 

 or priority of observation. I am fully conscious of my obligations 

 to the writings of those who have passed away, such as Darwin, 

 Sharpe, Sedgwick, Macculloch, Mchol, and Scrope, and, for informa- 

 tion, pubhc and private, to feUow-workers in England and on the 



^- E.g. that of thinking that the Twfc Hill conglomerate in North Wales 

 might be a member of the earlier Archaean series, and that the "newer 

 gneiss series " of the Loch-Maree district might overlie the limestone. 



