ANNIVERSARY ADDRESS OF THE PRESIDENT. 



I 99 



the Cheviots to the latitude of Burnt Island, and those same strata 

 south of the Tweed to the latitude of Harbottle and on towards 

 Rothbury &c., would seem to be due to comparatively small changes 

 of conditions ; and from the mapping by the Survey, Prof. Hull's sug- 

 gestion as to the origin of and difference between the calcareous and 

 true sedimentary or argillo-arenaceous strata, especially as exhibited 

 in the Upper Silurian, Devonian, and Carboniferous formations, appear 

 to be confirmed. Mr. Hull regards the true calcareous strata as dif- 

 ferent in origin and distribution from the other stratified rocks with 

 which they are associated, — not, indeed, properly coming under the 

 term sedimentary, this term being restricted to "gravels, sandstones, 

 shales, and clays," the presence of both classes of rock in the same 

 geological group being no argument in favour of their similarity. 

 Whenever interstratifications occur the limestones may be regarded as 

 occupying neutral ground between the respective areas of dispersion 

 of the sedimentary series. Could it be possible to trace the sources of 

 the "sedimentary" strata of any formation on the one hand and of the 

 limestones on the other, they would be found expanding in opposite 

 directions, this arising from the difference in the origin of the two 

 classes of stratified rocks, the calcareous being essentially organic and 

 the sedimentary essentially mechanical. We may, I believe, regard 

 the predominance of " sedimentary strata " as highly unfavourable 

 to the development of calcareous deposits in the same group of 

 rocks, from the fact of interference with the development of 

 life. 



Looking at the physical geology of Britain prior to the deposition 

 and distribution of the Carboniferous strata it is probable that " a 

 barrier of land existed, stretching from Wales eastwards, touching 

 the southern ends of the South-Staffordshire and Warwickshire 

 coal-fields, and including the Cambrian rocks of Charnwood Forest." 

 This barrier Prof. Hull believes was possibly an extension of 

 the Scandinavian promontory, stretching across the Irish Sea to 

 embrace the Cambro-Silurian districts of Wicklow and Carlow, and 

 dividing the Carboniferous rocks of South Wales, Somersetshire, and 

 Dean Eorest from the coal-tracts of Central and Northern England 

 and Scotland, the strata on each side belonging to two distinct 

 systems of distribution ; and their origin is therefore " due to two 

 different sets of oceanic currents " (Hull). 



The correlation of the Carboniferous rocks of Britain and Ireland 

 is even now a matter of difficulty and of difference amongst 

 those best able to decide. Even the continuous series between 

 England and Scotland from the Calciferous Sandstones of Eife, 

 south of the Cheviot, to the Yoredale series of Durham are most 

 difficult to correlate — much that has been called Carboniferous Lime- 

 stone being calciferous in one area and even Yoredale in the other. 

 The literature of the whole question is scanty and unsatisfactory 

 in the extreme ; and in the construction of my Tables these dif- 

 ficulties have met me everywhere. The wide difference that exists 

 in the mode of derivation and accumulation of the materials com- 

 posing the sedimentary series of the northern and southern groups, 



