o-li Itppek okdcVtcIan of The beiuvyk hills [vol. lxxix, 



phase of Lower Palaeozoic sedimentation, he thought the term 

 lagoon an unfortunate misnomer. Those who have searched 

 particular zones of graptolites in widely-separated localities, as. for 

 example, the Valentian of Wales, the South of Scotland, Scandi- 

 navia, etc.. well know that the lithology of the individual heds 

 which hold the fossils is as characteristic as the specific features of 

 the graptolites, and as widespread. The worker who knows his 

 rocks at one place will always he quick to find the fossils for which 

 he is searching at a new locality, although he may he hundreds of 

 miles away from the district where he got his knowledge. The 

 ' lagoon ' over the floor of which the famous continuous 4-inch band 

 with Mo ii or/ rapt us argent-ens was deposited must have been about 

 as wide as the Mediterranean Sea. The speaker could, however, 

 agree that the graptolites which one occasionally obtains from the 

 blue and blue-black mudstones, interstratified with volcanic ashes 

 and calcareous shelly beds all through the Ordovician formation in 

 Merioneth, are a meagre and ill-nourished lot, and that some 

 explanation of the dwarfed character of these faunas is required. 



Having experience that, in another district, in sandy calcareous 

 rocks which occur not far from the Ashgillian— Caradocian boundary, 

 certain species of the shelly fossils, which Mr. King had exhibited 

 as representative of his collections from the sandy beds above and 

 below the black graptolite- shales of the South- Western Benyvns, 

 occur associated together, he expressed the hope that, in the paper 

 when published, Mr. King would give information distinguishing 

 between the species which he regards as long-range fossils charac- 

 teristic of a particular kind of habitat, and the other mutating 

 forms which he has found distinctive of particular geological 

 horizons and really useful for zonal work. 



The Chairman (Prof. W. W. Watts) congratulated both 

 Authors on the presentation of the chief points of the two papers 

 in less than an hour. He regretted that Dr. A. Wade was unable 

 to be present to defend his reference of the Grwern-y-Brain shales 

 and limestone to the Ashgillian. Mr. King had confirmed 

 Dr. Wade's recognition of a peculiar fauna in these beds, but 

 referred it to condition instead of age. The speaker found it 

 difficult to understand what were the modern representatives of 

 the areas in which ' lagoon phases ' were supposed to have been 

 deposited. He was inclined to suggest that 'Black Sea conditions' 

 may have prevailed during the deposition of the Grwern-y-Brain 

 group. 



Mr. King, in reply, said that the conditions of deposition of 

 the black shales in question differed somewhat from the normal 

 graptolitic type. He did not suggest that all graptolite-shales 

 were necessarily of the same origin. He understood that the 

 : lagoons ' of Mr. Dixon were not in any way similar to the small 

 lagoons of coral-islands, but that they were essentially shallow- 

 water areas which were, for some reason, completely cut off from 

 the supply of normal sediment, and in which the conditions Avere 



