iv Huttori s Views of Igneous Rocks 173 



fluid mass, melted, but unchanged by the action of 

 heat." 



In this way, appealing at every step to the actual 

 facts of nature, Hutton built up the first part of his 

 immortal Theory. Most of these facts were more or less 

 familiar to men ; and some of the obvious inferences to be 

 drawn from them had been noted by several observers 

 before his time. But no one until then had grouped them 

 into a coherent system by which the earth became, as 

 it were, her own interpreter. The very obviousness and 

 familiarity of the doctrine at the present time, when 

 it is the groundwork of modern geology, are apt to 

 blind us to the genius of the man who first con- 

 ceived it, and worked it into a harmonious and luminous 

 whole. 



In the course of his journeys in Scotland, Hutton had 

 come upon many examples of rocks that were not stratified. 

 Some of these occurred among the Primary masses ; others 

 were observable in the Secondary series. Eeflecting deeply 

 on the probable reaction of the heated interior of the globe 

 upon its outer cooler shell or crust, he had come to the 

 conclusion that many, if not all, of these unstratified rocks 

 were to be regarded as material that had once been in a 

 molten condition, and had been injected from below during 

 some of the great convulsions indicated by the disturbed 

 strata. He distinguished three principal kinds of such 

 intrusive rocks " whinstone," under which term he 

 included a miscellaneous series of dark, heavy, somewhat 

 basic rocks, now known as dolerites, basalts, diabases and 

 andesites ; porphyry, which probably comprised such rocks 

 as felsite, orthophyre and quartz-porphyry ; and granite, 



