FORMATION OF BASALTE*. %6$ 



Gut the whole thickness of the mass, to vitrify the metallic 

 Fragments disseminated through the sand. 



These prisms extend to the length of 15 cent. [5*9 inch.] Figur*. 

 and from 1 to 2 or even 3 [0^9, to 0-/3, or 1*18 of an inch] 

 in diameter. They are parallel to each other, and have their 

 Axis, constantly perpendicular to the metallic stratum that 

 covers them. Though thenumber of their sides is not con- 

 stant, they are most frequently six. Their edges are sharp, 

 and pretty straight. Their faces are not strictly planes, but 

 a little concave ; and, what is remarkable, they appear to 

 have been more powerfully heated than the interior of the . 

 prism, a circumstance I conceive to be ascribed to the last 

 molecules of caloric, which have escaped as through so ma- 

 ny channels by the clefts or intervals, that were formed be- 

 tween the adjacent faces of the prisms. 



When these sandstones have not been so strongly heated, In some case* 

 VL r ■'. * .,..'.'. ,\i the charcoal 



the aggregation and prismatic division is not so well charac- arranged in oa- 



terised. Then too the charcoal, deprived of the air neces- rallcl strati, 



sary for its combustion, has arranged itself in longitudinal 



zones parallel with the axis of the prism, and so as to leave 



between them intervals of 2 or 3 millim. [0*787 or 1*18 of a 



line]. This singular phenomenon appears to me occasioned 



by the caloric, which, absorbed by the metallic stratum, 



taking the shortest course to reach it, and finding itself 



stopped in its progress by the particles of charcoal equally 



disseminated through the mass of sand, pushed them aside 



to the right ai/d left by imperceptible degrees to open itself 



apassage, and has thus dispersed them in little parallel strata 



or threads, as if they had yielded to the laws of affinity, 



which always tend to bring together homogeneal particles, 



when suspended by a fluid in a suitable state of rest. 



If we invert one of these masses of sandstone, it is a very T hi sandstone 

 good representation of the bottom of a basaltic stratum. In sake™ 

 short it is impossible to have a more perfect model of its 

 mechanical division*. 



Naturalists have already remarked clays, that have under-. more than any 

 gone a regular contraction in the tire : but, beside that silex observei/v 



* The piece I preserve in my collection is about 4 dec: [15 | inches 

 long, J and 2 dec. [7 inches and three quarters] broad, 



forms 



