THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 203 



As these films of carbonates occur only in the joints and 

 not as constituent parts of the rock, they must of course be 

 regarded as extraneous although characteristic matters. 



Geological Age. On this point farther information is still 

 wanting, — nevertheless we are not altogether without evidence of 

 considerable value. In the former paper it was shewn that the 

 principal contortions of the Lower Silurians of "West Cornwall 

 were produced before the deposition of the Ladock Beds — and 

 as the mica-trap partakes of these contortions in some places 

 — as at Victoria Point — it is evident that the rocks were erupted 

 before the contortions of the rocks of that period were com- 

 pleted. But it is certain that the traps cut through the Ladock 

 Beds also — both at Boscolla and near Penare farm ; it is 

 evident, therefore, that they are more recent in their origin 

 than these beds. The particular contortions of the stratified 

 rocks at Victoria Point — of which the mica-trap partakes, — 

 must therefore be referred to a later date, and are perhaps 

 merely local. 



But, as we have seen, the Ladock Beds appear to be of 

 Devonian and even of Upper Devonian age. It is true that the 

 exact date of the formation may be referred to almost any part 

 of that period, since as yet no fossils whatever have been found 

 in them. The stratigraphical evidence is however conclusive as 

 to their being more recent than the Lower Silurians and more 

 ancient than the final eruption of the granite. The mica-traps 

 are evidently newer than the Ladock Beds, since they cut 

 through them — they are as evidently older than the ordinary 

 elvans — since they are cut through by them, as at Treliske. But 

 it is generally held that the elvans were formed but little after 

 the final eruption of the granite — that is in early Carbon- 

 iferous times. Assuming therefore that the Ladock Beds are 

 Devonian, and the Elvans Carboniferous, we have good superior 

 and inferior limits for the mica-traps, and we may fairly enough 

 suppose them to have been erupted, or rather injected into the 

 Silurian and Devonian stratified rocks about the close of the 

 Devonian period, and to have been contemporaneous with the 

 great volcanic eruptions of the region to the north and east of 

 Bodmin, which are known to traverse upper Devonian rocks 

 near S. Petherwyn, and perhaps near Padstow also. 



