Vol. 63^] THE TOADSTONES OP DERBYSHIRE. 243 



etc. of North Derbyshire' 2nd ed. (1887) p. 140, the following 

 section is given : — 



Feet. 



1 . Black limestone "l q^ 



2. and toadstone J 



3. Black limestone 60 



4. Toadstone. 



5. White limestone. 



6. Toadstone. 



It is probable that No. 2 is the upper lava and No. 6 the lower lava 

 of the Fin-Cop area, and that No. 3 is part of the New Bridge Sill. 

 But in the Magpie Mine (op. tit. p. 141), a short distance south of 

 Sheldon, a shaft was sunk in the limestone through 738 feet without 

 reaching toadstone. About 200 feet north of the Magpie Shaft, in 

 an old quarry, the limestones are horizontal ; and about half a mile 

 to the south-east the dip is 5° southward. The depth of the shaft, 

 therefore, gives the thickness of the beds at right angles to the 

 bedding. 



As the bottom of the lower lava in the Miller's-Dale area is about 

 670 feet below the Toredale Series, and the shaft started below the 

 top of the Mountain Limestone, there is no doubt that the beds at 

 the bottom of the shaft are below the horizon of the lower lava of the 

 northern area. We may conclude, therefore, that the shaft was 

 sunk through the limestones which lie geographically between the 

 north- western and the south-eastern areas of volcanic activity. 



The Miller's-Dale and Matlock areas have not only a separate 

 volcanic history, but also a separate petrological one. In the former 

 the thin limestones with chert-bands attain a thickness of at least 

 400 feet, while in the latter they are only about 50 feet thick. 



II. The North- Western or Miller's-Dale Area. 

 (See Map, PL XIX.) 



The northern and most extensive of the three areas of volcanic 

 ■activity extends from Castleton on the north to Great Low on the 

 south, and from Buxton on the west to Ashford on the east, covering 

 a, superficies of about 72 square miles. 



The igneous rocks consist of at least two lava-flows, also of bedded 

 tuffs, vents, and sills. The two main lava-flows are separated by 

 a,bout 150 feet of limestone. There are, in addition, several small 

 outcrops of lava which I have not at present been able to correlate 

 definitely with the two main flows. 



The Upper Lava. 



The upper flow may be easily traced from a short distance west 

 of Litton Mill, in the railway-cutting on the southern side of the 

 dale of the Wye, thence along the railway to Miller's-Dale Station, 

 through the villages of Priestcliffe, Taddington, and Chelmorton, by 

 Nether Low to Great Low (over 4 miles from Buxton on the road 



s2 



