XVil 



precipitated from water flowing through the Great Adit, it can 

 scarcely be out of place to mention the quantity of detrital matter 

 deposited in the same neighbourhood ; a subject to which our at- 

 tention was directed from the chair, by Dr. Barham, in I860.* 



The valley of Carnon and its subordinate glens t drain an area 

 of nearly ten thousand acres ; J within which some thirty or forty 

 mines have been wrought, to greater or less extent, at different 

 times. In most of the water, whether mere drainage of the County 

 or purposely pumped to the surface, enormous quantities of various 

 ores are stamped and (dressed) washed ; the entire stream is, there- 

 fore, heavily charged with gravel, sand, and mud. || And, whilst 

 copper-mines were so largely worked in the district as they have 

 been of late, the rate of deposit was probably even more rapid 

 than it had previously been. At Higher Carnon, nearly two 

 miles above the present navigation, § some rather remarkable slabs 



* "In 1812 a crucifix [now in our museum] was found [in] Carnon 

 stream-works, about 30 feet under the bed of the river. You are aware that 

 crucifixes are, geologically speaking, of very modern date. The fact of its 

 being found 30 feet below the then existing bed of the river, seems to show, 

 more than anything else, the extreme rapidity with which deposits are formed 

 in certain favourable circumstances. We know that Carnon Valley is situ- 

 ated at the outlet of the great mining districts, from which the amount of 

 silt washed down is very considerable. The silt and gravel is from 40 to 50 

 feet deep. So that in this comparison of articles found, in connection with 

 the geological conditions in which they are found, we have two things to take 

 into consideration. First, the period during which the former sea-level has 

 subsided below the existing sea-level ; and in some places it appears that the 

 former was from 30 to 50 feet below what it is now. And, then, there is 

 another branch of enquiry. How long it would take to fill up these vaUeys 

 with this kind of silt ? "• — Baeham, Address to the Eoyal Institution of 

 Cornwall, Report XLII, (1860), p. 16.~- 



f Long within my recollection a tradition remained that cherry-trees 

 throve in the glen below Croft -handy. 



+ Thomas, Map of the Mining District between Camborne and Chacewater ; 

 History of Falmouth, p. 19. 



II " I have been told that about 70 years back \_i.e. 1708] the low lands 

 and sands under Perran Ar Worthal, which are covered almost every tide 

 with the sea, have on its going off, employed some hundreds of poor men, 

 women and children washing the tin-ore out of them." 



Peyce, Mineralogia Cornubiensis, p. 186. 



" If these waters be charged ordinarily with one part in three hundi-ed 

 of earthy matter (sometimes they contain more than double that quantity) 

 there will be brought annually into Eestrongett Creek about two millions and 

 a half of cubic feet. . . .besides immense quantities of gravel, which in times 

 of heavy rain are swfept along the beds of the streams and ultimately into 

 the navigation." — -Thomas, History of Falmouth, p. 51. 



§ " There is a tradition prevalent in the place and in its neighbourhood, 

 that the tide formerly flowed considerably farther up than Bissow-bridge." 



Fkancis, Gwennap, p. 7- 



