186 Reports and Proceedings — Geological Society of London. 



should see a small variety appearing among a number of forms not very different 

 from it, and from which it had been derived ; but when the variety had prevailed, so 

 as to be the dominant form, we were far on in the history of the species ; that it was 

 a great assumption to fix upon any bed we now know as representing the original 

 source of any group ; that we know too little about the chronological order of the 

 geological divisions referred to to reason with any safety on the migration of Grap- 

 tolites from one area to another; that the term Lower Llandeilo, for instance, was 

 very unsatisfactory as used in the paper ; there was nothing lower than the Llandeilo 

 Flags at Llandeilo ; and where older beds occurred in Scotland and elsewhere, 

 it was not at all clear that the equivalent of the Llandeilo Flasjs was present at all. 

 He differed also altogether from the author as to the position of the Dufton Shales, 

 and criticized the views of the author as to the range of some species. He thought 

 that M. Barrande's theory of the colonies was borne out by the study of the Grapto- 

 lites, but that we had not sufficient data to speculate as to the areas in which they 

 made their first appearance, or the order of their geographical distribution. 



Prof. Duncan observed that at the present time there was, among other forms, 

 quite as great a range of species as that of the Graptolites pointed out by tlfe author. 

 Having looked through all the drawings of Graptolites that he could meet with, he 

 had found none whatever that were accurate ; and he had moreover never in any 

 specimens discovered such cups or caliees between the serrations as were always 

 attributed to these organisms. From all he had seen he was led to the conclusion 

 that the projections on the Graptolites bore the same relation to the central stem as 

 those of some of the Actinozoa. These latter also, like the Graptolites, seemed to 

 prefer a muddy sea. Professor Duncan also suggested that the Graptolites were 

 really the remains of the filiform polypiferous parts of floating Hydrozoa. 



Prof. Morris regarded the paper as mainly suggestive. It was on all hands agreed that 

 there were in Britain two principal zones in which graptolitic life was most abundant ; 

 and the same held good in America. Both these seemed to be homotaxially related. 

 M. Barrande had long since pointed out the probable emigration of many of the 

 Bohemian species from the British area ; and there could be no doubt of there being 

 many species common to Europe, America, and Australia. This afforded strong 

 evidence in favour of some such theory as that of migration. He cautioned 

 observers as to taking careful notice of the manner in which Graptolites are presented 

 in their matrix ; for when seen from three different points of view, they exhibited 

 such differences that three species might be made from one form of organism. 



Mr. Gwyn Jeffreys mentioned the wide distribution of marine Hydrozoa by means 

 of winds and currents, as illustrative of the history of Graptolites, the dispersion of 

 which might have arisen from similar causes, and not from migration. 



Mr. Prestwich commented on the uncertainty of our knowledge with regard to 

 Graptolites, and consequently regarded speculation on the subject of their migration as 

 premature. He instanced Cardita planicostata, which was formerly regarded as 

 having originated in the Paris basin and come thence into England, but which bad 

 since been found in far earlier beds in Britain ; so that the presumed course of its 

 migration has been reversed. 



Mr. Hicks remarked that the rocks referred by the author to the Upper Cambrian 

 were in reality the lowest of the Silurian series, and that the Graptolitidse were 

 exclusively a Silurian family. 



Mr. Hopkinson also made some remarks both on the distinction of different species of 

 Graptolites and on their distribution. He regarded the Quebec area as that in which 

 these forms had originated. 



The Chairman commented on the great want of accord among those who had 

 studied Graptolites, not only with regard to their structure, but to their distribution 

 in different horizons. He thought that the suggestion of the author, as to modifica- 

 tion of form during migration having taken place, seemed to throw some light on the 

 subject. He could not regard two districts now only separated by the Sol way Firth 

 as constituting two geographical areas so distinct that the occurrence of the same 

 species in both could with propriety be held to be due to migration. The phenomena in 

 the other cases seemed to him quite as much in accordance with distribution from some 

 common centre as with migration along any line connecting two spots where Grap- 

 tolites are now found. He thought that the recurrence of these forms on different 

 horizons in Cumberland was to be accounted for by the fact that most of the rocks which 

 intervened between the shales containing these organisms were merely subaerial vol- 

 canic beds, on which, after submergence, these muddy shales had been deposited. 



