ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixxiii 



twenty or thirty species of other kinds of animals likewise identical 

 with species in the lower and similar beds just mentioned. Now 

 M. Barrande places this trappean mass with its included schistose 

 beds at the bottom of his upper division, and thus there are forty or 

 fifty species common to his two divisions*. It was justly remarked, 

 however, by Prof. M'Coy, that there seems to be no reason why 

 this mass should not be regarded as the top of the lower division, in 

 which case all the Graptolites would be contained in that division, 

 and the number of species of organic remains common to that and 

 the upper division would be reduced to tw^enty or thirty. The whole 

 number of species discovered by M. Barrande two or three years ago 

 was upwards of eleven hundred. These numbers would give between 

 two and three per cent, as common to the upper and lower Paleeozoic 

 divisions. Prof. M'Coy has made a similar estimate from the fossils 

 contained in the Cambridge Museum, and finds about fourteen or 

 fifteen per cent, common to the Upper and Lower Silurians, sup- 

 posing the May Hill and similar beds to be included in the Caradoc ; 

 but if these latter beds be placed, as Prof. Sedgwick and himself 

 have maintained they ought to be, in the Upper Silurians, he believes 

 that this per-centage might be considerably diminished. It is very 

 desirable that the palaeontologists of the Geological Survey should give 

 us an accurate estimate of the same kind, for it is only by a strict 

 numerical estimate, and not by general impressions, that we can 

 really decide how far our own country presents an anomaly when 

 compared with the perfectly developed but restricted region of 

 Bohemia on the one hand, and the wide field of North America on 

 the other. 



It will be a strong argument in favour of the new plane of separa- 

 tion between the two great divisions of the Silurian rocks, should the 

 discontinuity of stratification in Wales and the adjoining counties 

 which belongs to this period be found to coincide with that plane. 

 At present the evidence is in favour of this conclusion, for in every 

 case, I believe, in which the discordance has been observed, it is be- 

 tween the upper beds of the Caradoc and lower beds in the series. 

 It is to the corresponding epoch that I am at present disposed to refer 

 the m.ovement with which we are here concerned. In the North of 

 England, as I have above remarked, there is no evidence of a corre- 

 sponding movement. 



It appears singular that a geological epoch at which so extraor- 

 dinary a change took place in organic life over a large part of the 

 surface of the earth, should be one to which M. de Beaumont has 

 not been able to refer a single European line of elevation. After 

 this period, the bottom of the widely extended Silurian sea must 

 have remained, with the exception of a few particular localities, 

 comparatively horizontal, and ready to receive the deposits of the 

 Upper Silurian beds through the whole area of the "West and North 

 of England now under consideration. 



* Bulletin de la Societe Geologique de France, January 1851, p. 153. 



