I. GEOLOGY. 693 



Sandstone, and horizontal sections, on the scale of six inches to one mile (for 

 height and distance) illustrate the sheet. One showing the Dukenfield 

 Colliery and the various seams of coal through which the shaft is sunk ; the 

 other, the structure of the Manchester coal-field and adjoining country. 

 A vertical section, on a scale of 40 feet to an inch, of the Lancashire and 

 Cheshire coal-fields, shows the various seams of coal worked at Dukinfield 

 and other collieries, and the relative thickness of the sandstones, shales, and 

 other strata connected with them.. 



Horizontal and vertical sections descriptive of the Yorkshire coal-field are 

 also shown. 



32521. Geological Map of a portion of the Yorkshire 

 Coalfield (on the scale of six inches to the mile) ; the topography 

 by the Ordnance Survey, the geology by the Geological Survey of 

 England and Wales. 



The geological formations shown on'.the map are (top) Magnesian Limestone 

 (blue), Middle Coal Measures (black), Lower Coal Measures (pale black), Mill- 

 stone Grit (still paler black) ; in the Coal Measures and the Millstone Grit 

 thick beds of sandstone are denoted by yellow and other colours spread over 

 the general black tint ; the positions of faults at the surface are shown by 

 white lines, and where faults have been proved in workings, their corresponding 

 positions in beds of coal are denoted by yellow lines ; black lines are the out- 

 crops of coal seams. The depths of collieries, and where possible the thickness 

 of the coals passed through, and sundry other geological and mining details, 

 are engraved on the maps. In looking at the map it must be borne in mind 

 that its object is to show what rock it is that forms the surface at each spot, 

 and that the fact that the surface at different spots is formed of different rocks is 

 owing to the inclination of the strata. If the beds lay flat, we should have the 

 same rock extending over nearly all the area. But the beds do not lie flat ; over 

 a great part of the country they slope or dip in a general way from south-west 

 to north-east. In consequence of this dip the lowest beds, Millstone Grit, 

 come up to the surface at the south-west corner ; as we go thence in a 

 north-easterly direction the Millstone Grit passes away underground and is 

 covered up by the Lower Coal Measures ; these in their turn are carried down 

 and hidden beneath the Middle Coal Measures. The dip is steepest on the 

 south-west, and decreases towards the north-east till the beds become flat and 

 at last turn up and begin to dip towards the south-west, so that the measures, 

 as far as we can see them, lie in a basin. How far towards the east this basin 

 extends we cannot say, because, soon after the change of dip occurs, the 

 Magnesian Limestone conies on and hides the Coal Measures from view. 

 Besides the rocks mentioned the flats of alluvial river-muck and gravel are 

 distinguished by a pale straw colour ; old river gravels, deposited when the 

 rivers flowed at a higher level than now, by a reddish brown tint ; and some 

 few patches of Boulder Clay and Gravel by stippling. 



3252m. Index Geological Map of Wales, scale four miles 

 to one inch, being a reduction of the one inch Geological Survey 

 map of the same district. 



Vertical section of the Purbeck strata of Dorsetshire. 

 Vertical section of the Tertiary strata of the Isle of Wight. 

 Horizontal sections of the Isle of Wight. 

 Horizontal sections of Dorsetshire coast, &c. 



3252n. Geological Survey Map of Ireland, scale one 

 inch to one mile. 



