224 Proceedings of the Royal Physical Society. 



allowed to cool slowly they have acquired a stony structure. 

 Out of the basalts of the neighbourhood of Edinburgh and 

 the lavas of Sicily, Vesuvius, and Iceland, he thus produced 

 at one time glass, at another, lithoid masses (" crystallites " 

 as he called them) not unlike the original rocks. 



It would be beyond the scope of my present slight sketch 

 to enter more fully into these remarkable researches, or to 

 trace the course of Hall's subsequent career as an experi- 

 mental philosopher of a high order. Every one of his 

 memoirs is replete with original observation, careful induc- 

 tion, and suggestive speculation. In particular his memorable 

 essay on " The Effects of Compression in Modifying the 

 Action of Heat,"* formed the starting point for the long 

 succession of brilliant researches by which subsequent 

 observers, notably Delesse and Daubree, have thrown so 

 much light on the still obscure subject of metamorphism. 



The Scottish school of Geology, of which Hutton, Playfair, 

 and Hall were the three great founders, dealt with the grand 

 dynamical principles of the science rather than with ques- 

 tions of detail. Its range was necessarily much more re- 

 stricted than that which is now open to us. It knew almost 

 nothing of organic remains, and had no intimation of the ex- 

 tended vista into the past history of our planet which organic 

 remains have since opened up. Its most strenuous admirers 

 will not now contend for the accuracy of all its doctrines, nor 

 for the validity of all the arguments by which principles true 

 in themselves were sustained. As yet the facts of the science 

 were comparatively few, and our wonder should be, not that 

 these men fell into what we now know to be obvious errors, 

 but that with such limited experience they should have erred 

 so seldom, and should have attained to such breadth and 

 clearness of perception. In the domain of igneous action, 

 with which we are more specially concerned at present, they 

 showed that granite, and the series of rocks which they in- 

 cluded under the term "whinstone," have most certainly been 

 erupted from beneath, and have in many cases hardened and 

 otherwise altered the stratified masses through which they 

 rose. 



* Trans. Boy. Soc. Edin., vi., p. 71 (read June 3, 1805). 



