240 II. HICKS ON THE TRE-CAMBlil AN ROCKS OF ST. DAYIl/s. 



Discussion. 



Mr. Judd thought that Mr. Hicks had proved that there were at 

 St. David's two series of rocks older than the Cambrian, but that 

 whether these were of volcanic or of sedimentary origin, was doubt- 

 ful. He thought the author was right in not attempting to correlate 

 the rocks described by him with any foreign formations ; for, in the 

 total absence of palaontological evidence, the mere fact that both in 

 America and Europe the Cambrian strata were found to be uncon- 

 formably underlain by other rocks, was no proof whatever of the 

 contemporaneity of the latter in the two areas. 



Mr. Forbes had heard Mr. Hicks's paper with much interest, and 

 the more so from his having studied in Norway a series of rocks so 

 closely resembling the specimens shown on the table that it would 

 be impossible to distinguish them by the eye. Like the rocks of 

 St. David's, those in Norway were, from their stratigraphical posi- 

 tion, evidently older than the Cambrian ; but not being fossiliferous, 

 nothing definite as to their geological age could be determined. He 

 thought Mr. Hicks had done well in applying new names to these 

 rocks, rather than, as has been too often the case, calling all rocks 

 below the Cambrians Laurentian, especially as these rocks, as well 

 as those very similar to them which he had met with in Norway 

 and Sweden, were very different in penological character from the 

 original Laurentian rocks of Canada. 



Prof. Seelbt objected to the adoption of such names as had been 

 employed by the author, as standing in the way of the recognition 

 of the probable correlation of these beds with the older rocks of the 

 noith of Scotland. The northern crystalline rocks under altered 

 conditions of pressure might acquire the same structure as those of 

 AVales. 



Prof. Hughes, in reply to a question of Mr. Blake's, pointed out 

 that the strike of the Dimetian was nearly at right angles to that of 

 the overlying series, so that, although the bieadth of the patch 

 shown in the map was small, there was quite a sufficient distance 

 exposed across the edges of the beds (with a dip of 80°) to give the 

 thickness assigned to the series by Mr. Hicks. The thickness might 

 have to be corrected for other reasons, as it was difficult in such a 

 highly metamorphosed series to deteimine whether the most con- 

 spicuous divisional planes were in every case to be referred to 

 bedding. He thought there was much value in the suggestions of 

 Prof. Seeley, though they did not weaken the case brought forward 

 by Mr. Hicks. It was most unsafe to try to identify these rocks in 

 separate districts by lithological characters alone ; and it was true 

 that conglomerates at slightly different horizons near the base of 

 one and the same group might, especially when metamorphosed, be 

 mistaken for the commencement of a new series. Put in the case 

 before them other tests also had been applied, and other proofs of 

 unconformity were adduced, such as discordancy of strike, the 

 occurrence of fragments of the immed ately underlying group in the 

 overlying conglomerates, &c. He was unable to recognize any thing 



