Correqmuleiicc—Profi'Sfior T. G. Bonnoj. 187 



interior of the earth from the very first, aucl that it simply makes 

 its escape at a tremendous pressure whenever a way is opened for it 

 through the solid crust. 0. Fisher. 



Harlton. 



March 5, 1901. 



NAMES FOR BRITISH ICE-SHEETS. 



Sir, — May I suggest to Mr. Lamplugh that to propose names for 

 British Ice-slieets before proving that they have existed is rather 

 like counting chickens before the}^ are hatched. At present we 

 know neither the ancient extent of land-ice in our Island, nor in all 

 cases what are indisputable traces of it. Wliere faith is strong this, 

 no doubt, seems a detail, but to sceptics it appears important. 



If, however, we admit that there was an East British Ice-sheet, 

 " maintained and augmented principally by the snowfall upon its- 

 own sui'face," how are we to explain the presence of Scandinavian 

 rocks at Cromer and other places on our East Coast ? Of that ice- 

 sheet the Dogger Bank would be centre and highest part. This- 

 tract is crossed (a little north of its centre) by a line drawn from 

 Flamborough Head to the Naze of Norway. Over an area measuring 

 about 70 miles from east to west, and 12 miles in the opposite 

 direction, it rises above the ten-fathom contour-line (the minimum 

 depth being 7 fathoms). The twenty-fathom line is very near to 

 the other one at the south-west end, but then recedes from it so as- 

 to enclose a long bank which stretches in a north-easterly direction, 

 almost half-way across the North Sea, and the thirty-fathom line on 

 the northern side extends from the Yorkshire coast to Jutland. 

 North and north-west of this limit are soundings down to 49 fathoms, 

 and those over 40 fathoms are rather common. In the great channel 

 off the south-west of Norway they are often over 200 fathoms (for 

 particulars see this Magazine, 18*99, p. 282). Thus the ice of the 

 Dogger-fjeld (would not that have been a better name ? ) must have 

 descended from its central plateau down slopes about 250 feet in 

 vertical height on the north and north-west, and about half that 

 amount down those from the south-west to the south-east. This mass 

 of ice flowing outwards towards nearly all points of the compass, 

 and buttressed on the western side by the Caledonian ice, which it 

 would try to 'shoulder' in that direction, would surely defend onr 

 shores from the inroads of the Scandinavian ice-sheet, however 

 nimbly it might climb the steep slope of the above-mentioned 

 channel. Is it, then, a mistake to identify Scandinavian rocks in 

 East Anglia ; for if the Dogger-fjeld existed they could not have 

 travelled on floating ice ? 'i'- ^^- Ronney. 



CONCRETIONS OF CALCITE IN MAGNESIAN LIMESTONE. 

 Sir,— The well-known globular concretions from the Magnesiai! 

 Limestone of Durham occur in many collections under the name 

 of 'dolomite ' or ' magnesian limestone.' Professor Garwood, how- 

 ever, effectually showed (Geol. Mag., 1891, p. 43G) that tliese 

 concretions are due to the crystallization of calcite in a ground of 



