338 C. A. SUSSMILCH AND W. G. STONE. 



too far away to have been effected by them. One sample 

 taken from locality A on the map (Plate LV) yielded on 

 analysis 70*1% of silica. These cherts and dark claystones 

 &re so poorly stratified and are so crowded with joints that 

 it is difficult, except in a few places, to determine their true 

 dip and strike. Until quite recently it had always been 

 supposed that they were conformable with the Cave lime- 

 stone and geologically above it, and that they, therefore, 

 were a part of the Silurian series. A more careful field study 

 made by us this year resulted in finding a number of places 

 where the dip and strike departed widely from that of the 

 Cave limestone. The observed strikes range from N. 10° W. 

 to N. 45° E., the positions of some of these are shown on the 

 accompanying geological map. The strike of the Gave 

 limestone is about N. 20° W., while its dip is westerly at 

 from 60° to 65°. In some places, notably at A on the map, 

 the strike of the cherts parallels that of the limestone, but 

 the dip is easterly at a high angle, that is towards the 

 limestone, and in the opposite direction to the dip of the 

 latter. The general strike of the radiolarian cherts appears 

 to be about N. 45° B., while the dip is typically a very high 

 angle, in many places almost vertical. 



These facts strongly suggest that an unconformity exists 

 between the radiolarian cherts and the Silurian limestone, 

 and if this be so, then their relative positions suggest that 

 they have been brought together by overthrust faulting. 

 If these conclusions are correct then the overthrust parallels 

 the main axis of folding of the Silurian strata (N. 20° W.) 

 and the tangential thrust which produced it must have 

 come from the west. 



The probability of such an unconformity receives support 

 from another feature. The radiolarian cherts are intruded 

 by a large dyke of andesite; this intrusion is adjacent to 

 the contact of the cherts and limestones. If the radiolarian 



