MODE III. BASALTIN. 



sibly been taken away, you arrive at the sides 

 of those two enormous volcanic mountains, and 

 you come to masses of scoriag or of blistered 

 rocks, where, beyond doubt, we are near the 

 source of the current ; all the basalts which have 

 been followed upwards, made part of that cur- 

 rent. 2. A great number of those large basaltic 

 platforms which cover isolated mountains, dis- 

 play on their surface blisters, spongy scoriae, or 

 drosses, like those which are observed on the 

 best preserved lavas ; nor can we refuse them a 

 simitar origin. Some others of these platforms 

 repose on volcanic ashes. 3. Some isolated 

 eminences present, it is true, summits of black 

 basalt, compact, prismatic, destitute of those un- 

 equivocal signs of the action of fire which are seen 

 elsewhere ; but the greatest part of them stands 

 by the side of those platforms with scoriated sur- 

 faces of which we have just spoken : they once 

 formed with them a continued whole, and have 

 evidently only been divided from them by the 

 excavation of the valleys and ravines which now 

 separate them. They cannot have had a differ- 

 ent origin ; the corrosive action of time and the 

 elements must have destroyed the scorified bark; 

 only the compact nucleus would remain, de- 

 prived of the marks of the action of fire, as are 

 the interior parts of the greater portion of lavas 



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