OBSERVATIONS ON BASALT, &C. 173 



bafaltic columns, and alfo for (heir articulations. If we flip- Enumeration of 



facts and cir- 

 cumftances. 



pofe that a mafs of fluid bafalt has filled a valley to an indefi- hi 



nite depth and extent, the procefs of arrangement in its parti- 

 cles mull, be induced by the removal of its heat or moifture, 

 according as its folution is igneous or aqueous. This can only 

 be done by the action of the atmofphere on its upper furface, 

 and by the ground on which it repofes abforbing the heat or 

 moifture from its under furface. From the variations of the 

 atmofphere, its adiion muft be irregular ; and, from the per- 

 petual change of the parts in contact with the heated or moift 

 furface, its operations will always be nearly as a&ive as at firft, 

 allowance being made for its variations. But the abforption of 

 the ground will be regular, and regularly diminifhing in activity, 

 in proportion as the parts near the mafs approach nearer to the 

 fame temperature, or fame moifture, with the mafs above; and 

 its abforptions can only be carried on by its tranfmiffion of 

 heat or moifture to the folid rocks below. From thefe confi- 

 derations it feems evident, that the arrangement of the part of 

 the bafalt near the ground, will be begun with more energy 

 than it can be continued, and that the refults will be more 

 flow and regular than the arrangement induced by the perpe- 

 tual though variable aclion of the atmofphere. After the firft i- Radiated 

 flage in the procefs of arrangement has been performed, and Jj^f f ™™f 

 a ftratum, if I may fo term it, of the jafpedeous fubftance ex- 

 tended over the furface of the ground, there feems noreafon to 

 doubt that a number of radiated fpheroids would be generated 

 in it, which would probably have all their centres about the 

 fame diftance from the ground ; and, as the arranging power 

 undergoes a gradual diminution of energy, it is not probable 

 that two rows in height of them fhould be formed at once, as 

 that would indicate a hafty procefs, which had prepared a 

 greater mafs- of matter for their almofl fimultaneous formation. 

 From thefe confederations, there feems no improbability in fup- in one layer, 

 pofing, that in the arrangement of a mafs of fluid bafalt, a 

 fingle layer of radiated fpheroids would be formed, repofing 

 on the ground which fupported the mafs. 



I have already fiated, that when the radii of two fpheroids 2. Thefe would 

 came into contad, no penetration enfued, but the two M^ptShS^he 

 became mutually comprefled, and feparated by a plane, well places of fide 

 defined, and inverted with a rufty colour. I alfo fiated, that co:Ua(a » 

 when feveral fpheroids encountered, they formed one another 

 4 into 



