ii Desmarest's Observations on Basalt 59 



cliffs of the Irish coast, in short even among the truncated 

 summits of the interior, we see the operations of one or 

 more volcanoes which are extinct, like those of Auvergne. 

 Further, I am fully persuaded that in general these groups 

 of polygonal columns are an infallible proof of an old 

 volcano, wherever the stone composing them has a com- 

 pact texture, spangled with brilliant points, and a black or 

 grey tint." 



Here, then, was a bold advance in theoretical as well 

 as observational geology. Not only was the discovery of 

 Guettard confirmed, that there had once been active vol- 

 canoes in the heart of France, but materials were obtained 

 for explaining the origin of certain enigmatical rocks which, 

 though they had been found over a large part of Europe, 

 had hitherto remained a puzzle to mineralogists. This 

 explanation, if it were confirmed, would show how widely 

 volcanic action prevailed over countries wherein no sign 

 of an eruption has been witnessed since the earliest ages 

 of human history. 



Desmarest was in no hurry to publish his discovery. 

 Unlike some modern geologists, who rush in hot haste 

 into print, and overload the literature of the science with 

 narratives of rapid and imperfect observations, he kept his 

 material beside him, revolving the subject in his mind, 

 and seeking all the information that he could bring to bear 

 upon it. He tells us that in the year following his journey 

 in Auvergne, he spent the winter in Paris, and while there, 

 laid before the Intendant of Auvergne the desirability of 

 having the volcanic region mapped. His proposition was 

 accepted, and Pasumot, one of the state surveyors, was 

 entrusted with the task of making a topographical map of 



