8 Sir James Hall on the Consolidation of the Strata. 



gravel was entirely restored on both sides. The agglutinated mass adja- 

 cent to the dyke bore no resemblance to the result of calcareous petrifac- 

 tion ; scarcely ever gave effervescence with acid ; and, by its gradual ter- 

 mination, differed from any whinstone-dyke I have seen to penetrate the 

 strata ; for, in the ordinary case, the termination of the crystallite against 

 the adjoining aggregate through which it passes, is almost always quite 

 abrupt. 



" About a hundred yards higher up the valley of Aikengaw, there occurs 

 an agglutination similar to the last, though without any whin-dyke, and 

 sufficiently strong to resist the elements, by which the surrounding mat- 

 ters had been washed away, leaving the pudding-stone, or agglutinated 

 shingle, to stand up by itself, in a manner remarkable enough to have at- 

 tracted the notice of the peasantry as something supernatural, since they 

 have bestowed upon it the name of the Fairy's Castle. 



" Farther up the stream, other agglutinations occur frequently, as we 

 could see in little narrow glens cutting through the mass ; and higher still, 

 they are so numerous as to meet and convert the whole into one unbroken 

 mass of pudding-stone, occupying all that is exposed to view. 



" These very remarkable, and, to me at least, novel appearances, were the 

 first which suggested the idea, that the consolidation not only of this class 

 of conglomerates, but of sandstone in general, had been occasioned by the 

 influence of some substance in a gaseous or aeriform state, driven by heat 

 into the interstices between the loose particles of sand and gravel, where it 

 had acted as a flux on the contiguous parts. On considering what this 

 penetrating substance might be, and from whence it could have come, the 

 following circumstance presented itself to my recollection at the moment, 

 and promised to afford some assistance to these conjectures. 



" A few miles lower down the valley in which the above facts were ob- 

 served, at the distance of more than a mile from the sea, and between two 

 and three hundred feet perpendicularly above it, there occurs a crag of 

 sandstone, in which a numerous succession of strata are distinctly visible. 

 Several of these beds have yielded much to the action of the air, and, in 

 dry weather, exhibit a considerable white efflorescence, which has com- 

 pletely the taste of common salt ; and so remarkable is this circumstance, 

 that the rock has acquired, in the country, the name of Salt-Heugh. 



" Here, then, it immediately occurred to me, was probably the source of 

 an abundant supply of the elastic substance or fumigator, whose action as 

 a flux had been pointed out by the agglutinations in Aikengaw above de- 

 scribed. 



" I conceived, that, if there were at the bottom of the sea a bed of sand 

 and gravel, drenched with brine of full saturation, and that heat were ap- 

 plied to it from beneath, according to Dr Hutton's hypothesis, the first ef- 

 fect would be, to drive the water from the lowest portion of the sand, and 

 to convert the salt which remained amongst it, together with the sand, in- 

 to a dry cake. During this operation, or until the cake became quite dry, 

 the absorption of latent heat would prevent the temperature from surpass- 



