332 ME. 0. A. SHRUBSOLE ON TKIASSIC PEBBLES OF [Allg. I903, 



derived from the Ordovician. The frequency of their occurrence in 

 conglomerates illustrated the law of the ' survival of the fittest.' 



Dr. J. W. Evans doubted whether the source of the majority of 

 the pebbles could be nearly as distant as Normandy. He had an 

 opportunity of examining those of the Biver Beni, at the point where 

 it reaches the low country after traversing several ranges of the outer 

 Eastern Andes. Almost all the pebbles were such as might have 

 been derived from the last range, and very few could be identified 

 as coming from rocks 50 or 60 miles upstream. 



Mr. Whitaker did not see why the deposits should not have 

 come from different directions in different localities ; the pebbles 

 were too widespread to have all come from the same district. He 

 congratulated the Author on his attempt to solve the difficult 

 problems dealt with in the paper. 



Mr. H. AV. Monckton remarked that, although it was possible that 

 the pebbles in the Budleigh-Salterton and Bunter Pebble-Beds were 

 derived from various sources, there was one constituent, the liver- 

 coloured quartzite, which was of a singularly uniform character 

 and had a very wide range. Also they sometimes contained fossils, 

 more especially Orthis budleigliensis. He thought that this rock was 

 one well fitted to survive, and may have been handed on from one bed 

 to another. He suggested that the liver-coloured quartzite-pebbles 

 may have been worn into pebbles along some old coast-line, and 

 have been derived from shingle-banks now wholly destroyed. 



Mr. W. Gibson said he did not think that the paper covered a 

 sufficiently wide area. The Trias, he thougnt, should be studied as 

 a whole. 



Mr. A. E. Salter stated that, after carefully studying a large 

 number of Bunter pebbles, he had come to the conclusion that the 

 quartzite-pebbles were of less value in indicating the source of 

 origin of the beds in which they were obtained, than the much rarer 

 pebbles of other rocks found associated with them. Several kinds 

 of igneous rock were found, in addition to radiolarian chert with 

 intricate secondary quartz-veining, and pieces of dark rock con- 

 taining much tourmaline. The last two might very well have been 

 derived from the South-West of England. 



Prof. Watts remarked that there was too great a tendency to 

 judge the Bunter pebbles on the evidence of Budleigh Salterton and 

 the Midlands, while a large intervening area remained unconsidered. 

 A great factor, generally omitted, was that a pebble-bed extending 

 over hundreds of square miles could not be paralleled with any con- 

 temporaneous deposit now being laid down. The only possible 

 explanation was that the Bunter pebble-beds were not contem- 

 poraneous throughout the whole region. In short, the Triassic 

 zones were not vertical, but horizontal. 



After pointing out that several local types of rock were repre- 

 sented in the Bunter pebble-beds of the Midland area, the speaker 

 said that our knowledge as to what underlies the Midlands is as 

 yet fragmentary, but at all events it seemed difficult to believe that 

 pebbles from Britanny or the Channel Islands could have got past 



