i242 ME. H. H. ARNOLD-BEMEOSE ON [Aug. I907, 



This decision is, I think, amply confirmed by the valuable work 

 which has recently been accomplished by Dr. Arthur Vaughan and 

 other workers on the palseontological zoning of the Carboniferous 

 Limestone. In the discussion on Mr. T. F. Sibly's paper, read before 

 this Society on February 7th, 1906, on the Carboniferous Limestone 

 of the Mendip area, Mr. C. B. Wedd stated that 



' in Eastern Derbyshire the coral- and brachiopod-faunas of the upper part of 

 the Carboniferous Limestone agreed closely with the Dibunopkyllum-Zone of 

 Dr. Vaughan's classification .... All the Upper Limestone, at least down to 

 the second bed of toadstone, could be assigned with confidence to the upper 

 Dibunophyllum-Zone (D 2 ). This included nearly the whole of the limestone 

 exposed in the neighbourhood of Wirksworth, Cromford, Bonsall, Matlock, and 

 Derby, and all the strata seen in the inliers of Crich and Ashover.' x 



It appears, therefore, that the palseontological zoning already 

 accomplished is not sufficient to separate the limestone into divisions 

 thin enough to enable us to determine the platforms of volcanic 

 activity in the above-mentioned neighbourhood. On the other hand, 

 it is possible that the present paper, which is based upon the strati- 

 graphy and petrology, may be of some service to the palaeontologist 

 in his endeavours to zone the limestones. 



The district over which the toadstones are seen may be divided 

 into three main areas of volcanic activity, between which there are 

 no exposures of igneous rock. 



I. The North-Western or Miller's-Dale area (map, PI. XIX). 

 II. The South-Eastern or Matlock area (maps, Pis. XX & XXI). 

 III. The South-Western or Tissington area (map, PI. XXII). 



Ill each of these areas are lava-flows, bedded tuffs, and volcanic 

 vents ; and in the Miller's-Dale and Matlock areas several intrusive 

 sills as well. 



In the Miller's-Dale and Matlock areas the igneous rocks are, 

 with the exception of the Hopton Vent, entirely in the Mountain 

 Limestone, and two main lava-flows may be traced for a distance of 

 several miles. But in the Tissington area the igneous rocks occur 

 mostly in the Yoredale Shales (limestone-shales), and lava plays only 

 a subordinate part. The following are some of the reasons for 

 separating the Miller's-Dale from the Matlock area. In the former 

 the upper lava is the thicker and extends over a greater district 

 than tie lower, while in the latter the lower lava is the thicker and 

 extends over a greater district than the upper. In the Miller's-Dale 

 area the lavas are separated by about 150 feet of limestone, and 

 in the Matlock area by from 80 to 100 feet of limestone. The upper 

 lava of Miller's Dale is on a lower horizon than the lower lava of 

 Matlock, and the limestones above it contain at least two bands of 

 interbedded tuff. 



In the shaft of Dirt-Low Mine, half a mile east of Sheldon (map, 

 PI. XIX), three beds of toadstone were seen. In the Geological- 

 Survey Memoir on * The Geology of the Carboniferous Limestone, 



1 Quart. Journ. Geol. Soc. vol. lxii (1906) p. 379. 



