46 Mr. Ferguson on the 



are sponges.* His main results given in Mr. Ansted's words are these, 

 " It would seem as if the sponges, which under certain circumstances 

 had grown and flourished at the bottom of the sea, had been at succes- 

 sive periods covered up by fine calcareous mud, deposited gradually upon 

 them ; that the particles of fine mud, thus sinking gently from suspension 

 in the water, had barely penetrated below the suiface of the sponges, 

 resting upon them, but not flattening them by the pressure : and finally, 

 that owing to some chemical cause, a deposit of siliceous matter being in 

 progress, the particles of siles were attracted to these organic bodies, 

 themselves containing some portion of the same mineral. It appears that 

 we can in this way, and no other, account, with any degree of jilausi- 

 bility, for these three phenomena, viz : — first, for the existence of beds of 

 flint in the chalk : secondly, for the organic structure visible in the flints, 

 and the frequent occurrence of fragments of corals, shells, and zoophytes 

 imbedded in them : and lastly, that in some cases large silicified sponges 

 are found growing vertically, one upon another, to a height; of several feet 

 in the chalk ; and that sponges, now silicified, have often grown through 

 and over the shells of echini, or molluscous animals, and even of other 

 sponges.t'\ 



These theories of Dr. Buckland and Mr. Bowerbank, of which I have 

 given you an abstract, seem to be nearly all that is known about these 

 flints in their natural position, in beds in the geologic scale. They are, 

 as Mr. Ansted remarks, equally puzzling to the geologist, the chemist, 

 and the zoologist. But when they are found, as they are in Buchan, 

 overlying the granite, they form a geological problem as hard to solve as 

 their own substance. 



From our brief survey of the surrounding country, we saw that 

 the predominating rocks are the crystalline, and the stratified unfossi- 

 liferous. Only in one instance did we find a limestone, with organics, 

 (an ammonite) which might consequently belong to the secondary group. 

 Old Red Sandstone occurs at Aberdeen, again (certainly) 'at Gamrie, but 

 it has not been positively seen at any point between, although it has 

 been supposed that it may nevertheless envelope the primary rocks along 

 the coast, beneath the sea level. Oolite and Wealdenbeds occur in the 

 neighbourhood of Elgin. The distance between these beds at Llanbride, 

 and the flints of Buchan, cannot be less than between fifty and sixty 

 miles. Water-worn fossils of the lias occur at Blackpots, near Banff, 

 but there they are manifestly in a diluvial clay. The Old Red Sandstone 

 is the newest rock that is known to occur over all Banfi'shire ; conse- 

 quently the whole of this county comes between the deposit under con- 

 sideration, and the newer formations of Morayshire. 



This newly determined greensand of Cruden, is the only rock at all 

 approaching, in the geological sequence, the chalk beds from which the 

 flint boulders must have been derived. We are forced to conclude con- 

 cerning it, that if it is not in situ, it is at least not far removed from it. 

 * Ansted, I. p. 472, t Ansted, I. pp. 474, 475. 



