THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 191 



111 some of the localities now to be specified, eruptive rocks 

 are inserted on the maps of the Q-eological Survey, sometimes 

 coloured as " traps " at others as " elvans." Some of the veins, 

 however, were for the first time noted by Mr. Barnett and 

 others are here noticed for the first time. "We have numbered 

 the respective veins on the accompanying sketch map. 



No. 1 occurs a little to the west of Eoscreage Beacon near 

 St. Keverne. It crosses the lane a little above the ancient 

 mansion of Roscreage, which is now occupied as a farmhouse. It 

 is much decomposed near the surface, but moderately fresh 

 specimens may be got out by a little digging. The course of 

 the vein appears to be a little to the east of north, but as the 

 fields were covered with corn at the time of our visit in 1879, 

 we couid not trace it far. A slight depression in the fields seem 

 to mark its position here, as in many other places. 



No. 2 occurs in a little creek of the Manaccan Estuary on 

 the north side of the Helford Eiver, just north of Penare farm, 

 and about three-quarters of a mile to the west of the Nare 

 point. The dyke courses somewhat to the east of north towards 

 Pendennis Castle, cutting through the (here) moderately 

 inclined Lower Silurian slates, and the nearly horizontal con- 

 glomerates which rest uncomformably upon them in the manner 

 diagrammatically represented in fig 1.* The rock here as 

 elsewhere is concretionary and very fresh pieces may easily be 

 obtained 



Con^loiiieratf!. 



Slates. 



Fi^ I --Belo2v Penare Fai in. 



No. 3. About 3 miles up the Helford River, at a point 

 situate a few hundred 3'ards short of " Frenchman's creek," is 

 another dyke of this mica-trap of precisely similar character and 

 direction — -which apparently splits into two as it goes northward, 

 since two distinct branches are to be seen on the north shore of 

 the river. 



* The dyke is not seen actually cutting through the slates at this point, 

 except at extreme low water, and not always seen then. But a very short traverse 

 to the east or the west will soon satisfy the observer as to the accuracy of the 

 representation in fig 1. 



