VOL. XXXVI.] PHILOSOPHICAL TRANSACTIONS. 333 



loose stones must of course fall down ; and that where the strata had few or no 

 fissures, they remained entire, and so formed those very irregular arches so 

 much wondered at in these places : which seems a more probable origin, than 

 what others have hitherto proposed. The three rivers, as they are commonly 

 called, in Peak's-hole, are only some parts of tiie cave deeper than the rest, 

 and receiving all their water from the spring which comes from the farther end 

 of the cave. The water which passes through Pool's-hole is impregnated with 

 particles of lime-stone, and so has incrusted almost the whole cave in such a 

 manner, that it appears like one solid rock. 



The lead mines in Derbyshire are very various with regard to their courses. 

 One, into which Mr. M. went down, had two branches; one running to the 

 N. E. the other to the n. w : and, as he was informed, one of the best they ever 

 discovered ran due north. Their breadth and depth are full as irregular. The 

 bodies dug through to come at the vein, are generally lime-stone and black 

 shale. But it is uncertain which of the two is uppermost. Of two mines into 

 which he went down, in one they had dug first through 26 yards of lime-stone, 

 then through one of black shale : in the other, first through 42 yards of 

 shale, and then through 28 of lime-stone. The substances found mixed with 

 the ore, are 



1 . Chert. This is a kind of flint, which Dr. Woodward, in his Method of 

 Fossils, p. 21, says is so called, when found in thin strata. But in the peak, 

 the strata of chert are often 4 yards thick, or more. They are found in lime- 

 stone, and not always disposed in strata. Those which he took notice of, were 

 generally either black, or of such a colour as the inspissated juice of the buck - 

 thorn berries, which the painters call by the name of sap-green : whence they 

 are called green cherts and black cherts. 



2. Spar. This is composed of crystal mixed with other bodies. Those called 

 sugar-spars, have their crystallizations very small ; and thus, on crumbling to 

 pieces have the appearance of powdered sugar. There were two sorts of these ; 

 white and blue.* Dog-tooth spar is a white pointed spar, in form and colour 

 something resembling teeth. 



3. Cauk. This Dr. Woodward says, is a coarse talcky spar. But in that 

 substance which Mr, M. met with in this country, under the name of cauk, he 

 could not discover any flexibility or elasticity, which that learned writer has set 

 down as characteristics of talck and talcky bodies. It seems to be nothing but 

 spar incorporated with a coarse earthy matter.-j- When this cauk is mixed with 



* Fluorspar, a compound of lime, fluoric acid, and water. Fluate of lime, 

 t It is now known that cauk consists of the barytic eartli and the vitriolic or sulphuric acid. In 

 the new chemical nomenclature, this compound is tenned sulphate of barjtes. 



