752 



GEOLOGY. 



mineral character ; but in cases equally numerous, they have been transported from a 

 considerable distance, and even from the mountains of remote lands, from which they are 

 now separated by seas, which are thus proved not to have existed at the period of the 

 passage. The preceding remarks must not be understood as applying to every case of 

 drift, which is often a mere bed of gravel or pebbles. The surface of the drift frequently 



appears scooped out into deep 

 basin-shaped depressions, and 

 '. raised into corresponding ele- 

 vations, the difference of level 

 amounting to from one to two 

 hundred feet, the external aspect 

 presenting a series of tortuous 

 conical heaps with intervening 

 cavities, as if excavated by the 

 hands of Titans. These round - 

 topped tumuli are very common 

 in the northern part of the 

 Monument Mountain. western continent, as in the 



annexed view, taken from the neighbourhood of Monument Mountain, in the United 

 States; and in some instances they have been mistaken for artificial mounds, the 

 sepulchres of a departed race ! 



Along the eastern side of England from the Thames to the Tweed, extensive and thick 

 beds of gravel or loam are distributed, not only mantling lowland districts, but elevated 

 table lands, and capping insulated hills, covering the chalk of the Yorkshire wolds and 

 the crag of Norfolk and Suffolk. In the midland counties these accumulations are abun- 

 dant. " From Houghton on the Hill," says Mr. Conybeare, " near Leicester, to Braunston, 

 near Daventry, proceeding by Market Harborough and Lutterworth, the traveller passes 

 over a continuous bed of gravel for about forty miles ;" and throughout the red marl, lias, 

 and oolite districts similar masses occur, the peb*bly constituents consisting of the wrecks 

 of rocks of the most distant ages, and derived from remote localities. In the gravel depo- 

 sits of South Derbyshire there are fragments of almost all the English formations from 

 granite upwards to the chalk ; and it would not be difficult, according to the authority 

 just cited, to form almost a complete geological series of English rocks from many single 

 gravel beds. In Earl Spencer's park at Althorp, Northamptonshire, in the gravel used 

 for the roads, brought from an adjoining parish, there is a large proportion of chalk flints, 

 though at such a distance from the present limits of the chalk ; and on the oolite form- 

 ation near Northampton, there are fields as thickly strewed over with fragments of pure 

 white chalk, as the superficial soil is generally with the substance of the subjacent rock. 

 Sir Joseph Banks observed pebbles of porphyry in the gravel near the town of Dunstable, 

 in Bedfordshire, porphyritic rocks occurring at no nearer point than the Charnwood 

 Forest hills of Leicestershire. In various places the transported matter is highly metal- 

 liferous, yielding lead, tin, platinum, and gold, with many of the more valuable of the 

 precious stones, as the diamond, sapphire, ruby, and topaz. The native sites of these 

 products have been broken down and reduced to gravel, and their mineral wealth removed 

 with the debris. Lead is obtained from drift between lake Superior and the Mississippi ; tin 

 occurs in the gravel of Mexico and Cornwall ; and pebbles of lead are found under similar 

 circumstances in the vale of Clywdd in a sufficient quantity to be worth working. The 

 drift is also highly fossiliferous, containing abundant remains of quadrupeds, mostly of 

 extinct species, but belonging to extant genera, which are now however confined to regions 

 far distant from the sites where the fossil species are met with. 



