34 Connection between Geology and Agriculture in 



deed, Ijy carefully considering the rocks traversed by the rivers, 

 and the kind of finer sedimentary matter likely to be borne down 

 during floods, adding the relative amount of soil, in which there 

 is already much animal and vegetable matter, that may be trans- 

 ported at the same time, and a fair average estimate may be 

 formed of the relative agricultural value of alluvial lands. At 

 the heads of estuaries much alluvial matter is necessarily accumu- 

 lated, offering a more uniform character than it would otherwise 

 do from the deposit of estuary mud in such situations, nevertheless 

 presenting differences in the drier places according to the kind of 

 sedimentary matter borne down by the rivers which respectively 

 flow into them. The Bridgewater and Worle levels can scarcely be 

 considered alluvial in the ordinary acceptation of the term, since a 

 large part of them would appear regular detrital deposits upon 

 the bottom of an estuary in which creatures usually inhabiting such 

 situations lived and died, as they have done in many deposits now 

 forming rocks. These levels support considerable numbers of 

 fine cattle, and portions of them supply large quantities of cheese, 

 generally known as Chedder cheese, to Cornwall, Devon, and 

 South Wales. 



As connected with the economic geology of the district, we must 

 not omit to notice the sea and blown sand which is extensively em- 

 ployed as manure in different parts of it. It is, as we have seen 

 (p. 426), partly now thrown up and partly an accumulation at 

 various points when the relative levels of sea and land were dif- 

 ferent from those we nov\r find, the land having been apparently 

 raised. It was employed, as now, for agricultural purposes, 236 

 years since, as appears by Carew's Survey of Cornwall (1602). 

 Mr. Worgan, in 1811^ estimated the expense incurred for the whole 

 county in land-carriage for this sand at upwards of 30,000/. per 

 annum.* Dr. Paris states it to have been ascertained that 4000 

 horse-loads have been taken from Bude in one day.f Not only is 

 it carried from that place by the Bude and Launceston canal, 

 with its branch extending to Holsworthy, the chief commerce on 

 which is the conveyance of this sand, but it is conveyed over land 

 abundantly in carts, so that a considerable portion of the adjoin- 

 ing portions of Cornwall and Devon are supplied with it from 

 Bude. A good road has been constructed to Trebarwith Sands, 

 on the coast near Camelford, purposely for conveying the sand 

 there found into the interior. 



* View of the Agriculture of Cornwall, p. 128. Borlase cites a letter in 

 the Philosophical Transactions of April, 1675, in which the carriage of sand 

 is estimated at 32,000/. per annum (Nat. Hist, of Cornwall, p. 48). Taking 

 this sum and that given by Mr. Worgan as fairly accurate, and as Borlase 

 did not object to a similar charge for the carriage of sand in his time, it 

 would appear that it had remained nearly the sani^e for about 140 vears. 



t Trans. Geol. Society of Cornwall, vol. i., p. 193. 



