part 4] THE MILLSTONE GRIT OF YORK'sil I RK. 287 



XIII. Climatic Conditions. 



In all considerations of ancient climates the distribution of land 

 and water must play an important part, as was long ago pointed 

 out by Humboldt and Lvell, for it is the dee}) circulation brought 

 about by Polar currents and the corresponding spreading of the 

 equatorial waters towards the Poles which arc the fundamental 

 elements in bringing about equable distribution of surface tem- 

 peratures. How may this be applied to the Millstone Grit period? 

 If the conclusions at which I have arrived with regard to the 

 uplift of this great Northern Continent be correct, then the epi- 

 continental area upon which the lime-secreting animals of the 

 Lower Carboniferous had existed would have been considerably 

 reduced, and a southward recession of the northern boundary of 

 the ocean must have followed. Dr. A. Vaughan has shown l that 

 sucli a recession is observable in South Wales. The Lower Tour- 

 naisian shore is represented on the map drawn up to illustrate his 

 paper as an embayment connected with the south-western channel, 

 which at its northern limit extended to the Clee Hills. In Upper 

 Visean times the shore-line of the south-western channel ran just 

 north of Bristol and continued in a straight line to Pembroke. 

 The whole neck of land which contained the ' Barrier ' shifted 

 with a wave-like motion southwards as Visean times proceeded. 

 Whether this uplift of land excluded the oceanic waters altogether 

 from the circumpolar regions at any time is not clear. The collec- 

 tions made by Col. H. W. Feilden, of the Nares Polar Expedition, 

 and described by R. Etheridge, 2 obtained chiefly from lat. 82° 40' X.. 

 clearly established the occurrence in these high latitudes of Car- 

 boniferous Limestone rocks. The facies is North American and 

 Canadian, although many of the species are British. 



In the paper by Col. Feilden and C. E. De Ranee (op. cit.) t it is 

 stated 



4 that a continuation of the direction of the known strike of the limestones of 

 Feilden Peninsula, carried over the Polar area, passes through the neighbour- 

 hood of Spitsbergen, where this formation occurs, and contains certain species 

 identical with those of the Grinnell-Land rocks of this horizon.' (P. 560.) 



The explanation of the presence here of Carboniferous Limestone 

 is somewhat difficult, except that it may be accounted for by an 

 opening from the Carboniferous ocean of North America, so giving 

 communication for the passage of those species which arc' identical 

 with those of the Carboniferous Limestone of North America. 



Etheridge, in the paper above cited, pp. 573-74, says : — 



' No Triassic strata have been detected either in this or any previous 

 expedition; whether, therefore, either the Permian and Trias seas, or both, 

 aided in the denudation of the Carboniferous group, or their sediments were 

 deposited and then denuded before the deposition of the Lias, which rests 

 upon the Eglinton-Island Carboniferous Limestone, must still remain an un- 

 determined question. It would therefore almost appear that it must have 



1 ' Avonian Shore-Lines ' Rep. Brit. Assoc. Manchester, 101."). pp. 429 31. 

 a Q.J. G. S. vol. xxxiv (1878) pp. 568-639. 



