278 



ME. H. H. AENOLD-BEMEOSE ON 



[Aug. 1907, 



is the intrusive mass, the more nearly it approaches a basalt. The 

 larger is the mass, the coarser-grained it becomes ; but, towards the 

 margins, it passes into a fine-grained dolerite or basalt. 



The lavas up to, or through which, some of the sills penetrate are 

 mentioned in the table. No intrusive rock known in the county 

 penetrated the limestones up to a greater height than about 400 feet 

 below the top of the Mountain-Limestone Series. 



Name of 

 Sill. 



Lava, up to 

 or through 



which 

 penetrates 



Coarse- 

 grained 

 Dolerite. 



Ophitic 

 Dolerite. 



Sub- 



ophitic 



Dolerite. 



Large 



Felspars 



with small 



Augites. 



Dolerite 



with 



granular 



Augites. 



Ba- 

 salt. 



Peak ] 

 Forest. ) 







X 



X 





X 





Potluck. j 



lower 

 northern area 





X 



X 



X 



X 





Water- ") 

 swallows. ) 



Do. 









X 



X 





Tideswell > 

 Dale. $ 



Do. 





X 





X 



X 





New ") 

 Bridge. ) 







X 



X 



X 



X 





Ible 







X 











Bonsall... > 



lower 

 southern area 



X 



X 



X 



X 



X 





High-Peak) 

 Tavern. ) 















X 















Low Farm. 















X 



YI. Summary and Conclusion. 



Since the year 1783, when William Withering 1 gave an analysis 

 of tw T o mineral substances, namely, the Rowley Rag and the Toad- 

 stone, much has been written on the Derbyshire toadstones. 

 Attempts have been made to prove that either three or only one 

 bed of toadstone extended through the whole district of the Mountain 

 Limestone of Derbyshire. The results of the investigations detailed 

 in this paper, and on the accompanying maps, show that the 

 toadstones must be divided into two groups : those contemporaneous 

 with the Limestone and Limestone-Shales, and others which were 

 intruded at a later period. The former consist of volcanic vents 

 with lavas and tuffs, and fall geographically and geologically into 

 three areas of volcanic activity distinguished by their extent, and 

 by the horizons of their main lava-flows and tuffs. The north- 

 western or Miller's-Dale area is the largest, and in many respects is 

 similar to the south-eastern or Matlock area ; while the Tissington 

 or south-western area contains the latest phase of contemporaneous 

 volcanic action, which was continued into the Yoredale Series. The 

 majority of the vents are composed of volcanic agglomerate; but 

 the Calton Yent near Miller's Dale is a typical basalt, with a small 



1 Phil. Trans. Roy. Soc. vol. lxxii, pt. ii, pp. 327-36. 



