264 GEOLOGY AKD AKCH^EOLOGY OF COENWALL AND DEVON. 



elusion that both systems were in existence before the close of the 

 Triassic era. 



A further inspection shews that where the dikes intersect, — and 

 the instances are by no means few — those having a north-and-south 

 direction always cut through the east-and-west system : a fact 

 from which it may be safely inferred that the former are more 

 modern than the latter, that the joints they occupy are of different 

 ages also, and that whilst those running east and west may perhaps 

 be pre-triassic, the transverse system came into existence during 

 the New-Red era. 



The facts just enunciated are well seen in vertical sections ; 

 but a ground-plan or bird's-eye view discloses something more. It 

 then appears that the east-and-west dikes — those intersected — are 

 faulted, and traversed by longitudinal veins of carbonate of lime, 

 which come up to, but stop short of, the north-and-south dikes. 

 Their continuity is interrupted by the latter, but is immediately 

 resumed on the other side. Here, again, we may draw a few per- 

 fectly trustworthy inferences : First, that a considerable interval 

 of time elapsed between the formation of the east-and-west dikes 

 and that of those which cut through them ;— an interval sufficient 

 for the former to become coherent, to be themselves, as well as 

 the rocks containing them, jointed and faulted, to be fissured 

 longitudinally without affecting the integrity of the walls along 

 the various divisional planes, and for the fissures to be filled with 

 calcareous matter by precipitation. And, second, that it is im- 

 possible to deny that in some cases at least, joints are due to an 

 agency utterly unlike desiccation.* 



Whilst there appears to be no flaw in the logic by which the 

 foregoing conclusions are reached, it would be of great interest 

 to get some additional facts, — facts which probably not only exist, 

 but are abundant in a county which, like Cornwall, is rich in 

 veins and dikes ; and, if it may be done without presumption, I 

 venture to commend the subject to, and to request the co-operation 

 of, the geologists of the county. 



The Lotver Silurian Fossils of Cornwall: — As long ago as 1837, 

 Mr. Peach discovered fossils in the quartzites near Goran Haven, t 



* See Trans. Devon. Association, Vol. i, 1863, pp. 31 — 43. 



f See Trans. Royal Geol. Soc. Cornwall, Vol. vi, pp. 317—326. 



