304 Geological Society* 



thickness cannot be less than 350 or 400 yards. It is ge- 

 nerally a pure calcareous freestone, of a whitish yellow co- 

 lour, disposed regularly in very numerous strata. These 

 consist either of very white marble, or of aggregations of 

 small rhombic crystals : towards the top it is very con)pact 

 and porcellanous. Few of the Ijeds arc without organic 

 remains: in some are found small anomias, in others en- 

 trochi, or turbinated shells, cornua anmionis, nautih, and 

 branching coralloids. This rock is superficially cracked, 

 so as to present a columnar appearance. Beneath it is 

 much rent, and abounds in shake-holes and large caverns 

 with water-swallows. Some of the fissures connected with 

 the surface are filled with clay sand and quartz pebbles. 

 The veins are filled principally with calcareous spar, heavy 

 spar, and fluorspar: they also contain iu their upper part 

 galena, calamine, manganese, red iron ore, white china 

 clav, and steatite. 



Upon the fourth limestone lies the third loadstone. The 

 most eastern basset of this rock is at Bonsall upper town. 

 Its thickness in different parts is very various, from four 

 feet to eighty yards. Its usual appearance is that of a 

 cavernous stony mass, of a dirty purplish brown hue. 

 Often it is of a dark blue colour with shining specks, as 

 hard and sonorous as cast iron, also of a light green or 

 blueish gray colour, and rarely it appears as a gritty yellow- 

 ish stone called Duastone. Its structure when recent is 

 amygdaloidal, the cavities being filled with green or white 

 globules of calcareous spar. The veins in the limestone 

 above and below this stratum have rarely if ever broken 

 through it ; but rents proceed from these into the top and 

 bottom of the toadstone, in which galena and the usual 

 veinstones are sometimes found. 



Third limestone. — The most eastern basset of this rock 

 in the line of section is on the western slope of Masson 

 Tor. Its average thickness near Matlock is about 80 yards. 

 Its colour varies from gray to brownish black. It includes 

 several beds of limestone, with layers of dark gray nodular 

 chert. Its organic remains arc numerous, and it abounds 

 in mineral veins that aflTord galena, calamine, and blende, 

 embedded in calcareous spar and heavy spar. 



Second toadstone. — The most eastern basset of this rock 

 is in the bed of the Derwcnt. Its' average thickness is 

 greater than that of the third toadstone, and it does not ap- 

 pear liable to such variations of thickness as that rock. In 

 external characters it does not greatly difler from it, except 

 that it contains narrow veins of fibrous calcareous spar. 



Second 



