554 W. S. Gresley — Boulders in a Coal-seam. 



All the stones seem to be composed of very similar rock, the 

 colour outside being grey, blotched with black. The extei'ior for 

 a depth of about ^ inch, is of a darker shade than the interior of the 

 stones ; due no doubt to being so long in contact with the coal. I 

 cannot detect any signs of fossils upon or within any of them. 



From No. 2 a slide has been prepared, which I submitted to 

 Prof, Bonney, and he has been kind enough to send me the following 

 description of it : — " A very compact pale grey quartzite, consisting 

 of rather angular fragments, often about "01 inch diameter, of quartz, 

 with which are a few more rounded grains of a decomposed kaolin- 

 like material, which probably were once felspar ; these have worn 

 out of the slide in grinding. There are apparently a few specks of 

 iron-oxide, but some of these may be mere accumulations in the 

 above vacuities of the material used in grinding the slide. I note 

 also a few flakes of colourless mica, a small grain or two of epidote, 

 and one, partly broken away, which I think is tourmaline.^ The 

 rock macroscopically and microscopically is like some of the more 

 compact quartzites in the pebbles of the Bunter in Staffordshire, and 

 in the Loch Maree district ; it differs in some respects from the 

 quartzite of Hartshill, the Lickey, or the Wrekin. It reminds me 

 of a quartzite pebble described by me some years since from the 

 Coal-measures of South Staffordshire, of which, however, I do not 

 possess a fragment for comparison. See Geol. Mag. Vol. X. p. 289." 



The seam of coal from which these boulders were taken is, 

 at this colliery, particularly subject to "Horses" or "Wants," 

 i.e. sudden interruptions in the continuity of the coal, its place 

 being taken by sandstone and shale, exhibiting current-bedding, and 

 often enclosing patches of detrital coal, &c. This coal-bed is here 

 and there swelled up to double its ordinary thickness, and again, 

 hard by, is reduced to half its proper thickness. It is also often 

 mixed with layers or patches of sandstone, having a concretionary- 

 looking formation, which set in and run out in a peculiar way. 



The roof of the seam is very variable in composition : sometimes 

 it is sandstone-rock, sometimes shale containing numerous strings 

 and pipes of bright, glossy coal, and some clay-ironstone nodules. 

 Again it is fire-clay or soft carbonaceous shale and coal mixed. [A 

 roof richer in fossil plant remains I never witnessed in any colliery, 

 and they are often exceedingly beautifully preserved. I have 

 obtained specimens of the leaflets of ferns (the actual dead leaves 

 themselves) and placed them between bits of glass to preserve them, 

 which when exposed to a current of air, flapped up and down, 

 though still fast by their stalks to the rock.] I mention all this to 

 show that the conditions under which this Coal-seam and its roof 

 were deposited were such as clearly indicate that currents of running 

 water, having considerable weight and velocity, flowed at the time of, 

 or immediately subsequent to, the formation of the Coal-seam ; and as 



^ I liave identified this mineral in a compact grey qiiartzite very like the above, 

 which is among the Bunter pebbles, and find a grain of it in a slide cut Irom a 

 similar quartzite which occurs on the Torridon road about three miles from 

 Einlochewe. — T. G. U. 



