330 report— 1879. 



progressive general subsidence, in which the central and northern barriers were 

 slightly implicated, and this extraordinary crust movement was to continue during 

 the accumulation of over 3,000 feet of coal measures and other deposits, all subaerial 

 in their method of formation, or having collected in shallow water or swampy ground. 

 These products of denudation and of organism succeeded each other time after time ; 

 great gravels, shales, and sands were intercalated, and even traces of some of 

 the rivers of the age are to be found breaching the seams. The more the subject, 

 commonplace as it may be thought, is considered, the more astonishing does it 

 become, for "the regularity of the subsidence and its amount must have kept pace 

 with the thickness of the accumulating deposits. That there were many long 

 intervals of quietude in the earth's crust may be gleaned, not only from the thick- 

 ness of many coal seams, but also from the subaerial denudation which occurred. 

 For instance, high up in the eries in this district, is a mass of red sandstone which 

 covers the denuded middle measures beneath; and this red rock of Rotherharn, 

 the result of coal measure denudation and removal, accumulated during the early 

 days of the upper coal measures, for it is lower in the geological series than some 

 members of the uppermost coal measures. 



Before the close of the age, marine conditions occurred in the rock, and a 

 limestone with goniatites was formed ; but still coal seam formation proceeded 

 until a totally different series of crust movements commenced in this country. 



The flexures which were produced at the close of the Carboniferous age had 

 their long axes east and west ; they suffered denudation and on the worn edges of their 

 strata rest the ' used-up Carboniferous ' — the lower Permian. Elsewhere, resting 

 apparently and often really conformably on the Carboniferous strata, the Permians 

 accumulated until great north and south curvatures occurred and produced the 

 Pennine chain. 



The denudation of the anticlinal or upward curves of the north and south 

 flexures progressed, and the coal measures, once continuous across England, were 

 worn off along the back-bone of the country and from off the east and west ridges 

 also. Vast as was the destruction and removal, there was still more compensa- 

 tion in nature, for faulting occurred on a large scale, and the measures were in 

 many places sunken down below the level of possible subaerial denudation. 

 It is to the pre and post Permian crust movements in producing basins and in 

 uptilting the formerly horizontal seams, and to the subsequent faulting, that we owe 

 the preservation and the possibility of reaching and working much of the coal of 

 this country. 



It appears that the position of this town refers quite as much to some remark- 

 able faults, and the results of the past Permian uptilting, as to the presence of the 

 river Don. Two important lines of fault run almost parallel, the one traversing 

 the centre of Sheffield, and the other being to the north of the outcrop of the 

 Silkstone coal. They pass, nevertheless, in a north-easterly direction, and the 

 country between them is much broken. Moreover, by a combination of the 

 results of uptilt and faulting, the strike of important coal seams has been so altered 

 that they encircle the town on the south, west, and north. The mineral products 

 have thus been brought within the reach of those by whose industry this town has 

 increased in size and population. 



With regard to the lithology of some of the great series just mentioned, it may 

 be suggested that the condition under which the beautiful limestones of the 

 Avon, and the dark, shaly, muddy, calcareous deposits of the corresponding 

 age accumulated in Scotland, were very different. The stone in the southern 

 example is many-coloured, and is nearly an organic deposit, whilst the shaly strata 

 of the northern series have crowds of calcareous fossils in them. Remove the shaly 

 substance, however, and consider and compare the fossils of both localities, and no 

 satisfactory distinction can be drawn between the depths at which they may have 

 accumulated. 



Both deposits contain crinoids, polyzoa, brachiopoda, and simple and compound 

 hydro-corals. The same occur in the limestones to the north of the central barrier, 

 which are intermediate in the arenaceous condition between those just mentioned. 

 It is admitted that the mineral condition of the original deposits has altered, and 



