internal Structure of the Magnesian Limestone. 105 



1st. Drotherton^ near Ferrt/ Bridge.— In the rail-roads and quarries of this place, the beds 



are exposed in the following order, beginning with the lowest. 



Feet 



1. Red marl and gypsum, surmounted by a few feet of blue clay 



2. Soft, yellow, earthy limestone, which effervesces feebly with acids 3 



3. An irregular bed or congeries of thin beds, imperfectly concretionary, partly") 



earthy, and partly compact, very difficult of fracture, of various shades of V 3 

 colour, with a blue tinge near the centre 1 



4. Thin, greyish beds, with layers of bluish or ash.coloured marls 6 



5. A bed similar to No. 3 j 



6. Many thin, shattery beds with the separating marls ; of these beds some are") 



porous or cellular; some are compact; the structure is variable. Thecolours ( 

 (sometimes exhibited in cloudy spots, and sometimes in stripes,) are grey, ( 

 yellowish grey, or brown J 



At the top are some very thin beds resembling marl-slate. 



2nd. Knottingley. — In the cut for the canal below the village, the bottom earthy beds (No. 2.) 

 of the preceding section were laid bare. Near the centre of the system there were some remark, 

 able contortions, which had brought up the lower gypseous marls ; and in the highest portion 

 of the same section were some thick, cellular and concretionary fetid beds, of a dark, smoke-wrey 

 and bluish grey colour, and entirely unlike all the other parts of the series. This locality is also 

 interesting from its exhibiting the junction of the top beds of the deposit with the upper red 

 marl ; but the contortions of these beds make the phaenomena less instructive than might have 

 been anticipated*. At the tAVo last-mentioned localities none of the strata contain much ma.". 

 nesia, and the greater part of them do not exhibit a trace of it ; yet in other quarries in the 

 same neighbourhood, and in the same geological position, magnesia is an essential constituent of 

 the rockf. 



3rd. Limestone-Hill on the xoest side of Tickkill.—'ThG beds are in the following order, 



beginning with the lowest. t- . t , 



° ° rcet. Inches. 



1. A grey, close-grained dolomite, hard and translucent at the edges, lustre "1 



glimmering, fracture uneven, and fragments irregular j 



2. Very thin, irregular beds ; some nearly compact and glimmering; others") 



dull and earthy; colours grey, smoke-grey, and yellowish, grey ; | 

 separated by many natural joints coated with dendritic impressions, S3 G 

 and parted by very thin seams of light-coloured bluish or yellowish | 

 marls J 



3. A hard, irregular bed of dolomite ; concretionary; cellular; of various") 



shades of colour, and coated over with dendritic impressions ; glim- I . 

 mering ; part nearly compact and porcellaneous, part granular and | 

 porous J 



4. Thin, shattered beds like No. 2 3 



* See Plate VII. fig. 6. 



t Subordinate to the above deposit arc occasionally found some thin beds which contain a 

 larger proportion of magnesian earth than any other part of the whole series. From a specimen 

 derived from a quarry south of Robin Hood's Well, Mr. Holme obtained the following result. 



Carbonate of lime 29.75 



Carbonate of magnesia 60.25 



Alumina and red oxvd of iron 7.75 



Silica ' 1-25 



Water 1-00 



100 grains. 



VOL. III. — SECOND SERIES. P 



