part 4] AtfD GEOLOGA' OF COREIS AND aberllefEjsni. 543 



graptolite-shales is known. The fineness of the sediment counts for nothing - , 

 as it may be paralleled in certain unquestionably shallow- water groups : for 

 instance,' some beds in Modiola-phnses. The same may be said of the organic 

 remains, restricted to plankton and nekton, but often teeming in individuals. 

 Under lagoon- conditions, I have suggested, such kinds of sediment and 

 organisms, though unusual in ordinary shallow-water beds, would tend to 

 accumulate. 



' Radiolarian cherts (of the striped type) and graptolite- shales go together, 

 in my opinion, in their relations to standard deposits and to the contempo- 

 raneous shore-lines. So far as radiolarian rocks are concerned, I have been 

 able to get further evidence ; but, as regards graptolite-shales, I have had, 

 perforce, to be content with studying the work of others. In 1911 Arthur 

 Vaughan, when collaborating with Prof. S. H. Reynolds on Burrington Combe, 

 considered the rapid variation shown by graptolites to be more probably the 

 result of an in-shore life than of a pelagic existence ; but a shallow-water 

 origin has rarely been ascribed to particular graptolite-beds : I can recall 

 merely one example, described about 1921 by G. T. Trcedsson. On the other 

 hand, the association in some places, such as Tourmakeady (described in 1909 

 by C. I. Gardiner & S. H. Reynolds) of coarse grits with radiolarian cherts 

 and graptolite-slates is irreconcilable with sedimentation in deep seas, as, in 

 the case of the cherts, had been pointed out already by A. J. Jukes-Browne. 



' The kind of evidence that has been desired, so far in vain, has been a 

 determination by field-mapping of the relations of a graptolitic deposit to the 

 shelly beds on the same horizon, and to the contemporaneous shore-line. 

 Hitherto it has been assumed that the graptolitic phase indicates the deeper 

 water. If, as I understand, Mr. King has obtained proof by his mapping 

 that the area occupied by certain graptolite-beds lies between that of the 

 contemporaneous shelly beds and the independently-known position of the 

 shore-line, he has made an important step towards harmonizing a number of 

 anomalous observations in a way which may vitally affect our conceptions 

 of Older Pahsozoic geography.' 



Prof. 0. Holtedahl was interested to hear Mr. King's sugges- 

 tion that the graptolitic shales were shallow-water sediments 

 because graptolite-shales have cpiite commonly, until recent times, 

 been regarded as indicating deep-water conditions. The speaker 

 had, as a result of his studies on Ordovician sediments of a certain 

 district of the Christiania region (published in 1909), come to the 

 conclusion that the graptolite-shales there were not of deep-water 

 origin. Prof. J. Walther had, before that time, expressed the 

 opinion that the black shales, so commonly found in the Cambro- 

 Silurian formations of North- Western Europe, were deposited in 

 lagoon-like bodies of water; but Ave must certainly assume these 

 to have been cpiite extensive epicontinental seas. The sea in 

 which the Cambrian alum-shales of the Scandinavian Peninsula 

 were deposited must have had a length at least comparable to that 

 of the peninsula itself. As to the stratigraphical conditions just 

 at the Ordovician-Silurian boundary, it was interesting to notice 

 how they are in the Christiania region very similar to those 

 mentioned by Mr. King. In some districts there seems to be an 

 unbroken succession, but with passage-beds of a very coarse 

 character, while in others distinct breaks are noted. 



Prof. W. Gr. Fearnsides said that, with regard to Mr. Dixon's 

 suggestion that graptolite-bearing mudstones represent a ' lagoon ' 



