260 SIR. H. H. ARNOLD-BEMROSE ON [Aug. 1907,. 



Haddon the massive limestones with intercalated toadstone are 

 faulted against thin beds of limestone with chert. The fault runs 

 from south-west to north-east. 



A short distance north-west of Bakewell a lava is brought up 

 by a small dome in the limestone. It is separated from the 

 cherty limestones by about 40 feet of massive limestones, and is,, 

 therefore, apparently on a higher horizon than the upper flow of the 

 Matlock area. 



The Position of the two Main Lavas in the Series. 



The three sections quoted in the Geological-Survey Memoir on 

 North Derbyshire (pp. 22, 23) from Whitehurst (a.d. 1778), Pilking- 

 ton (1789-1803), and Farey (1811), are based upon the assumption 

 that there are three beds of toadstone extending throughout the 

 Mountain-Limestone area (in addition to ' chance ' beds). They 

 agree in placing the upper toadstone 150 feet down in the limestone. 

 Two of them separate the first and second toadstones by 150 feet of 

 limestone, and the third (namely, Pilkington) considers that 138 

 feet is correct. Their estimates of the thickness of the second 

 toadstone vary from 90 to 240 feet. Two of them mention a third 

 bed varying in thickness from 66 to 90 feet, and about 200 feet 

 below the second bed. It is interesting here to note that John 

 Whitehurst's third bed (66 feet thick) is according to his section,. 

 pi. i, 1 the Shothouse-Spring bedded tuff described below (p. 263). 

 This section also shows a shaft sunk into a very thick bed, which 

 may be the Grangemill Yent. Pilkington's third bed is the agglome- 

 rate of that vent ; and the second bed of ' blackstone/ mentioned 

 by Pilkington as being 240 feet thick at Snitterton, was probably 

 the lower lava-flow and a portion of the Bonsall Sill. In connexion 

 with the latter opinion, it may be mentioned that Sir Archibald 

 Geikie considered that the ' blackstone ' at Snitterton might 

 represent part of a sill. 2 



The curious coincidence of 150 feet of limestone separating the 

 lava-flows in both the Miller's-Dale and the Matlock areas led me 

 to make several measurements of the limestone-beds. The result 

 of those in the north-western area I have stated above (p. 250). 

 The conclusion at which I have arrived is, that for the south- 

 eastern area 150 feet would be too high a figure. 



Near Jughole Wood, over half a mile north of Bonsall, the 

 limestones between the two lavas are between 83 and 112 feet thick. 

 Two other measurements on the northern slope of Masson Hill gave 

 101 and 110 feet respectively as a maximum. In Lathkill Dale the 

 two lava-flows are separated by about 87 feet of limestone. The 

 measurements were carried out with the barometer corrected for 

 changes in the weather, due allowance being made for the dip of 



1 'An Inquiry into the Original State & Formation of the Earth' 4to. London, 

 1778. 



2 'Ancient Volcanoes of Great Britain' vol. ii (1897) p. 22. 



