74 HISTORY OF GEOLOGY AND PAL/EON TOLOGY. 



inadequate, and it was incontestably proved that crystalline 

 rock might originate from molten rock when slowly cooled 

 under pressure. 



Hall also conducted experiments on the bending and folding 

 of rocks. He spread out alternate horizontal layers of cloth 

 and clay, placed a weight upon them, and subjected them to 

 strong lateral pressure. These and similar experiments have 

 been often repeated within recent years, and it is well known 

 that in this way phenomena of deformation can be artificially 

 produced which bear the closest resemblance to the phenomena 

 of rock-deformation under natural conditions. 



Hall, in his desire to vindicate Hutton's theory, became 

 himself one of the great founders of experimental geology. 

 At the same time, John Playfair, 1 whose interest in geology 

 had been roused by Hutton's companionship, became the 

 enthusiastic exponent of Hutton's theory. 



It was Playfair's literary skill that opened the eyes of scien- 

 tific men to the heritage Hutton had left for them. He did 

 for Hutton's teaching what fifty years after was done for 

 Darwin's doctrines by the gifted Huxley. The brilliant ex- 

 ponent and successful combatant, no less than the deep 

 student and enlightened thinker, is required to establish a new 

 system of thought, for such a system is always, bound to be in a 

 measure reactionary to older doctrines that have received the 

 stamp of usage and authority. 



Playfair's Illustration of the Huttonian Theory (1802) is a 

 lucid exposition of that theory in the form of twenty-six ample 

 discussive notes. Playfair's work differs in no essential point 

 from the views held by his master and friend, but many 

 subjects which receive a subordinate treatment in the Theory 

 of the Earth are brought into prominence by Pbyfair, and 

 placed for the first time on a firm scientific basis. 



Among the subjects fully discussed are the uprise and 

 bending of strata, the origin of crystalline rocks at low 



1 John Playfair, born 1748, in Bervie, Forfarshire, son of a minister, 

 showed in his early years a remarkable genius for mathematics. He 

 studied in Aberdeen and Edinburgh, in 1773 became minister in Bervie, 

 in 1785 Professor of Mathematics in the University of Edinburgh, and 

 twenty years after Professor of Philosophy in the same University. Led 

 by Hutton into the study of geology, he devoted his holidays to geological 

 tours throughout Great Britain and Ireland, and in 1815 and 1816 made 

 longer tours to Auvergne, Switzerland, and Italy; he died in 1819 in 

 Edinburgh. 



