THE ORIGIN OF LAKES. 219 



use in a somewhat different sense in the case of lakes is 

 not Hkely to give rise to any confusion, and there is no 

 objection to adopting the usual classification of lakes into two 

 divisions, namely, the lakes which are contained in rock 

 basins, and those which are not, though perhaps a four- 

 fold division would be more useful, the lakes being classified 

 according as they occur (i.) in craters, (ii.) in depressions 

 which have been blocked up by some material, (iii.) in areas 

 which have been depressed by earth movement, and (iv.) in 

 hollows of erosion ; this latter classification I propose to use 

 in the present paper/ 



(i.) Crater lakes. — The existence of lakes occupying the 

 site of volcanic craters has long been known, and their 

 origin is quite apparent. Many crater-shaped hollows are 

 ready to receive water, after the cessation of volcanic action; 

 the Lucrine Lake and Avernus are classical examples of 

 lakes formed in this manner. Several crater lakes of the 

 volcanic region of Central France have been sounded by 

 M. Andre Delabecque, and their symmetrical shape and 

 considerable depth shown (2}. Lac d'Issarles in the depart- 

 ment of Ardeche has a depth of 108 metres, Lac Pavin 

 of 92 metres, Lac de Tazanat of 66 metres, and Lac 

 Chauvet of 63 metres. The three last-mentioned lakes are 

 in the department of Puy de Dome, and their boundaries 

 and subaqueous contours are remarkably circular. Con- 

 cerning Lac d'Issarles, Scrope writes that it is one of those 

 lakes which " differ from ordinary craters, not only in their 

 greater dimensions, but in the nature also and disposition 

 of their enclosure, which is usually of primary, or, at all 

 events, pre-existing rocks, merely sprinkled more or less 

 copiously with scoriae and puzzolana, little if at all elevated 

 above the surface of the surrounding country " ; it thus 

 becomes clear that crater lakes may lie in hollows formed 

 by explosion or by accumulation of volcanic ejectamenta, or 

 by a combination of the two processes. 



1 I had written this article before reading the admirable chapter upon 

 lakes in the second edition of Sir John Lubbock's Scenery of Switzerland^ 

 where a similar classification is proposed. I hope all who are interested 

 in the question of lake-formation will refer to that work. 



