250 a sill and faulted inlter in tideswell dale. [may 1 899, 



Discussion. 



Mr. Strahan regretted that he had never himself visited the spot. 

 He enquired whether this was not the first recorded instance of an 

 intrusive igneous rock in Derbyshire, and congratulated the Author 

 on this addition to his valuable work in that county. The alteration 

 of the rocks below the intrusive sill was such as might have been 

 effected by a contemporaneous lava-tlow ; he had not clearly under- 

 stood to what extent alteration had been observed in the overlying 

 strata also. It was curious that the dolerite had so closely con- 

 cealed itself between sheets of toadstone, and he hoped that further 

 search on the part of the Author might reveal other occurrences. 



Mr. E. S. Herries also spoke. 



The Author replied to Mr. Strahan that the first recorded sill 

 in Derbyshire was mentioned by Sir A. Geikie in his ' Ancient 

 Volcanoes of Great Britain.' The limestone above the sill at Peak 

 Forest is marmorized, but not to so great a distance as the lime- 

 stone lying below the sill in Tideswell Dale. In the latter place, 

 the bed of lava above the sill has probably prevented the lime- 

 stones on the top of it from being altered. 



