1883.] of the rocks of Guernsey. 387 



Norman Battery, do we find a slaty rock with a steep dip N. E. by 

 N. Still further N. in a projecting bluff, some bands weather out 

 dipping about 30 \V. N. W., and at the very extremity of the 

 island under Fort ])oyle itself, a series about 20 feet thick of 

 slaty beds dip 60° or 70° N. E. No dips can be obtained along 

 the rest of the const, and none of the inland quarries afford any 

 appearances that can be trusted. Thus then the only really 

 strong evidences of dip in the beds of northern area would carry 

 them above the gneiss, and the rest are on the one hand in 

 themselves weak, and on the other hand not inconsistent with 

 this view. 



In pages 7G and 77 of Vol. in. of the Society's proceedings it is 

 mentioned that in a quarry on the W. side of Delancy Hill a bed 

 of stratified quartzite dips to the N.W. This dip also would 

 favour a superior position of the rocks in which it occurs. But it 

 cannot be trusted. The quarry is now abandoned, and occupied 

 by water, so that the bed cannot be reached. But observation 

 shows that the main bed splits up on the right hand side into 

 several thinner beds, which can be traced by the eye for many 

 yards along the quarry- face, and which fork out and re-unite in a 

 manner inconsistent with true bedding. One or two of these thin 

 seams pass up to the summit of the cliff and, after a little trouble 

 I succeeded in obtaining some specimens. These do undoubtedly 

 possess a strong l'esemblance to a sandstone. But the entire 

 absence of quartz from the general rock of the quarry was very 

 suspicious ; and the anastomozing arrangement of the veins was 

 quite inconsistent with stratification. While I was revolving the 

 possibilities of its being a fissure filled up, or a vein of segregation, 

 a slide submitted to Professor Bonney, without any indication of its 

 origin, was pronounced by him to be ' Probably igneous, allied to 

 granite.' This exactly agrees with the whole behaviour of the rock. 

 Those who are familiar with White Trap and other decomposing 

 dykes will have no difficulty in comprehending the mistake. 



We have in this case a good instance of what I have several 

 times remarked before, that behaviour in the field is the surest 

 evidence for the nature of a rock, and next to that, microscopic 

 examination of a section. The appearance of hand-specimens is 

 inferior in value to either. 



Yet another line of argument may be taken up. It is clear 

 that the gneiss has been subjected to immense transverse pressure. 

 The generally vertical foliation, the abrupt flexures, the crushed 

 condition of the beds, unite in testifying to this. Whatever force 

 produced this must have acted simultaneously on all rocks then 

 existing. If these northern rocks be, as Ansted calls them, older 

 metamqrphic rocks, this pressure would have affected them too, 

 and could hardly fail to have developed in them a cleavage. Not 



