116 REPORT — 1861. 



kaims. He repudiated the notion of their formation by glaciers. He considered 

 they were due to the action of water, as indicated by their internal structure ; and 

 supposed that they must have been formed by the waters of the ocean, when they 

 stood at least 800 feet above its present level. The only question, as he thought, 

 was, whether they had been thrown up as submarine spits or banks, or whether they 

 had been formed hj a process of scooping-out, when the land emerged from the 

 ocean. His opinion wavered between these two views ; but he was inclined to the 

 former. In the east of Scotland, these kaims had mostly one direction, viz. east 

 and west; and as they were in various positions, sometimes on level land and 

 sometimes on sloping hills) he thought that a sudden lift of the country out of 

 the ocean would better produce that uniformity of direction than any other view, 

 and also occasion the scooping-out and removal of materials, leaving continuous ^ 

 ridges. 



On Isomeric Lines, and the relative Distribution of the Calcareous and Sedimen- 

 tary Strata of the Carboniferous Grouji of Britain. By Edwaed Hull, 

 B.A., F.G.S., of the Geoloyical Survey of Great Britain. 



The author refeiTcd to the observations of Prof. Phillips in Yorkshii-e in reference 

 to the carboniferous rocks, from which it appeared that the calcareous portions 

 attained their greatest vertical development towards the south-east, while the 

 sedimentary strata of the Yoredale series and millstone grit increased in thickness 

 towards the north-west ; and the author went on to show that what was true in 

 Yorkshire on a smaller scale, was also true on a larger scale for the whole of the 

 carboniferous rocks north of the old barrier of laud which stretched across Central 

 England dm-ing the Carboniferous epoch. 



It was shown that the carboniferous limestone was most fully developed in 

 Derbyshire, attaining a thickness of about 5000 feet, and from this as a centre it 

 thinned away westward and northward, so that in Scotland the thickness was only 

 about 250 feet, in some places even less than this. 



On the other hand, it was shown that the sedimentary strata (sandstones, shales, 

 &c.) were of greatest thickness in Lancashire, and from this thinned away east- 

 ward, southward, and partially westward. The thickness of these sti-ata in Lanca- 

 shire (12,500 feet) had probably once been exceeded in Scotland, where, reasoning 

 from analogy, Mr. Hull concluded the whole carboniferous group, excluding the 

 limestones, had once reached 14,000 feet, previous to the denudation which has 

 swept away the uppermost members of the coal-measiu"es*. 



These variations in thickness of the sedimentary strata were indicated by the 

 isometric lines on the maps exhibited to the Section, and are accounted for on the 

 g-roimd that, throughout the Carboniferous period, a large tract of land had existed 

 in the North Atlantic, from which the sediment had been derived and spread over 

 the bed of the sea by a current coming from the north-west. In consequence of 

 this, the sands and clays would gi-adually lessen in quantity the further they were 

 canied, and thus they would be deposited in greatest force towards the north-west, 

 and in least towards the south-east, where there would be a clear sea. 



On the other hand, the limestones, being due to the labours of marine animals 

 which required an ocean free from mud for their full development, were formed in 

 gi'eatest force in Derbyshire, and from this as a centre diminish in thickness west- 

 ward and northward. Thus in Scotland they are on the point of disappearing, 

 being replaced by a vast thickness of sedimentary strata altogether wanting in 

 Central England. These variations were indicated by a second system of isometric 

 lines, indicating the propagation of the calcareous rocks from Derbyshire as a centre 

 in a series of waves of constantly diminishing force. It would thus be seen that 

 the two sets of isometi-ic lines above refen-ed to would intersect each other from 

 nearly opposite directions. 



To account for these opposite developments, the author showed that they arose 

 from the necessity of things ; that the marine animals (as the corals and crinoids), 



* These results were borne out by admeasurements of the beds in several counties, which 

 are published at length in the Joui'nal of the Geological Society of London, vol. xviii. p. 127. 



