TRANSACTIONS OF SECTION C. 331 



it is possible that much impurity may have heeu removed by percolating car- 

 bonated waters from the purest of the limestones. And, indeed, unless this is 

 credited, it is impossible to compare some of these old marine sediments with any 

 bow forming on the floor of the sea. All the known calcareous sea floor deposits 

 contain a very considerable percentage of silica and other matters, and if the 

 Carboniferous limestones were ever in the condition of modern deep-sea ooze, in 

 order that they should have looked like the chalk they must have lost, in some 

 manner or other, more than 35 per cent, of impurities. So far as I can understand, 

 much of the Carboniferous limestone may have accumulated at no very great depth 

 and on banks within the scour of currents, and their prevalence would account for 

 the comparative absence of sandy sediments in some situations. No traces of Atoll 

 formation exist. 



With regard to one or two late discoveries relating to the organic remains of 

 the Carboniferous limestones, it is necessary to refer you to Moseley's important work 

 amongst the Tabulata. These must now be removed from the true stony corals, 

 and some will be relegated to the Hydrozoa, and others to the Aleyonaria. It is 

 a fact of great interest that Sorby should have noticed that whilst the modern 

 true corals are built up of carbonate of lime in the form of arragonite, the great 

 tabulated forms of old are composed of calcite. 



Quite lately Mr. Busk has been investigating the large polyzoa of the genus 

 Heteropora, and I saw, under his manipulation, that this recent and Crag group, 

 with strong palaeozoic affinities, is so constructed that the branching tubular or- 

 ganisms of the oldest rocks with perforations in their walls and tabulae must be 

 included amongst species of genera closely allied to it. 



A host of ill-defined tubular forms, such as the Stenoportc, will thus find a final 

 zoological resting-place. 



The arenaceous series of the Carboniferous formation in England are not less 

 wonderful than the Calcareous. They thin out very rapidly from 10,000 feet in 

 the Burnley district to 100 close to the central barrier in Leicestershire, and it 

 would appear that the sea drift was from the present region of the North Atlantic, 

 along the shores of the swampy coal-plant growing land. 



The arenaceous deposits to the south of the central barrier have the same general 

 relation 'as those to the north, and the grits of the Welsh and Bristol coal-fields are 

 silicious, and were in all probability derived from the Silurian and Old Red rocks 

 to their north-west. The culm measures of Somersetshire and Devonshire — those 

 thick deposits with impure thin coals with limestones towards the bases — are of the 

 age of the upper parts of the Carboniferous limestones and of .the grits of the central 

 area. The evidences in this age of the denudation of granite and other silicious 

 lands, and of more or less distant diffusion of the sediment, extend far and wide 

 from the United Kingdom, a belt of similar rocks being found in south-western 

 and central Europe. It is, moreover, very probable that the upper Vindhyau rocks 

 ofHindostan, those fine sandstones and grits which have yielded the building-stones 

 to the great Gangetic cities, are of the same relative age (or slightly older) as 

 the strata of which so many Yorkshire towns are mainly built. 



Whence came the thousands of feet of the sands and shales of the coal 

 measures ? is as yet a question which cannot be answered. It appears that very 

 widely distributed deposits of the same kind are comparatively rare amongst them, 

 and that most of the organic deposits, as well as the inorganic sedimentary, do not 

 extend over great breadths, but are more or less lenticular in shape, or thin out 

 or become changed in their lithology. This fact and Sorby's suggestion that the 

 currents which deposited the strata had not any definite course rather tend to the 

 belief in the former presence of a vast delta during that ancient aspect of nature. 

 It is certain that some of the vegetation which subsequently became coal, and many 

 feet of the roof above, were not always formed with great slowness, for stumps and 

 trunks of trees have been found standing where they grew, with their roots in 

 their under-clay and their stems wrapped round with coal, and the shale and gravel 

 above. Moreover, in some places, a series of these interesting relics exists, one set 

 being placed above the others. 



With regard to the coal itself, varying as it does in its physical peculiarities, 



