384 Geological Society. 



In these pits the measures are fully developed, and consequently 

 the variations may be explained by the thinner beds not having been 

 equally included. In the Madeley list every thin seam is given. 



The shales and sandstones vary greatly in their characters, tliough 

 the former are said to be more uniform than the latter, and to contain 

 layers of argillaceous carbonate of iron. A bed of freshwater lime- 

 stone occurs in the upper part of the measures, at Inet, the Frog's 

 Mill near Nordley, and at Tasley. It is very hard, has a fine con- 

 choidal fracture, and varies in thickness from one to two yards. A 

 minute account is then given of the changes presented at different pits, 

 and it is shown that the thinning out of the strata of sandstone and 

 shale is frequently of great advantage to the miner by bringing into 

 contact, beds of coal, which would otiierwise be separated many feet. 



Carburetted hydrogen is disengaged in greater abundance from the 

 lower than from the upper measures, and in greatest quantity on 

 commencing a new work, especially on approaching a fault, when 

 large masses of coal are constantly blown off the main beds with loud 

 reports. Carbonic acid gas is rarely found in a pit at work, and Mr, 

 Prestwich suggests that the quantity sometimes noticed may have 

 been accumulated in adjacent old pits. 



The mineral contents of the coal measures are confined to the ar- 

 gillaceous carbonate of iron, sulphuret of iron, sulphuret of zinc and 

 petroleum. The celebrated spring, which once yielded more than a 

 hogshead a day, produces now only a few gallons a week ; but another 

 abundant spring has been discovered, and considerable quantities of 

 petroleum have been obtained in working the Dingle pit. Titanium is 

 found in considerable quantities in the hearthstones of the old furnaces 

 often beautifully crystallized, but in greatest abundance in a massive 

 state. In analysing some crystals of sulphuret of zinc found in the 

 coal measures the author detected titanic acid. 



6thly. New red sandstone. — Only the lower divisions of this forma- 

 tion occur in the immediate neighbourhood of Coalbrook Dale, flank- 

 ing the eastern and north-western sides of the field, and in some places 

 abutting against the dislocated edge of the coal measures. They con- 

 sist of clay, marl, and sandstones, overlaid by calcareous conglo- 

 merates, to which succeed coarse sandstone, marls, and other conglo- 

 merates. The lowest beds pass conformably into the coal measures, the 

 line of distinction being chiefly distinguishable by the change in the 

 colour ; but some of the vegetable remains of the coal may be, though 

 rarely, detected in the sandstone series. Mr. Prestwich is of opinion 

 that there is a want of conformity between the lower and upper systems 

 of the new red sandstone series. 



7thly. Trap rocks. — The greater portion of the Wrekin, Arcol, Mad- 

 dox, and Lilleshall Hills, &c. are composed of greenstone, felspar rocks, 

 and amygdaloid. Smaller bosses also rise to the surface at variou.s 

 points within tlie coal-field, and others have been discovered in the 

 deep workings ; but it is worthy of remark that no trap has been no- 

 ticed in any of the crevices or fissures connected with the faults. The 

 trap does not appear to have charred the coal; but at New Hadley, 

 at a point where a boss appears at the surface, the coal in its vicinity 



