1907-1908.] 



7 1 



In recent years Mr, Arnold-Bemrose has made a most 

 exhaustive study of the extinct volcanoes of Derbyshire, and has 

 published the results of his investigations in two valuable papers 

 read before the Geological Society of London. In his earlier 

 paper of 1894 "On the Microscopical Structure of the Carbon- 

 iferous Dolerites and Tuffs of Derbyshire," he stated that the 

 Toadstones were then generally admitted to be contemporaneous 

 with the Carboniferous Limestone; shortly afterwards, however, 

 on taking Sir Archibald Geikie over some typical parts of the 

 district, the latter pointed out that while some of the toadstones 

 were contemporaneous with the limestone, others were intrusive, 

 and some represented the vents through which the volcanic 

 material was brought to the surface. 



During the past twelve years Mr. Bemrose has mapped the 

 toadstones on the 6 inch ordnance maps, in some places on the 

 25 inch, and has examined many hundreds of new thin slices of 

 rocks ; the results of this laborious investigation are given in his 

 paper on "The Toadstones of Derbyshire; their Field-Relations 

 and Petrography," Quart. Journ., Geol. Soc, Vol. LXIIL, 1907, 

 pp. 241-281. He now divides the toadstones into two groups, 

 one contemporaneous with the limestones and limestone shales, 

 the other intruded at a later period, showing that Whitehurst's 

 inference regarding intrusion was partly right. 



The contemporaneous group consist of volcanic vents with 

 lavas and tuffs, the majority of the vents being composed of 

 volcanic agglomerate. The lavas are vesicular and amygdaloidal 

 in structure, and often much decomposed. They contain Olivine, 

 Augite, Felspars, Magnetite, and Oxide of iron. The intrusive 

 sheets or sills consist mostly of ophitic olivine dolerites. 



The local term " Toadstone " is supposed to be derived, either 

 from the fancied resemblance of the amygdaloidal varieties to the 

 back of a toad, or else to be a corruption of the German 

 " Todtstein " (dead stone) in allusion to these rocks being barren 

 of lead ore, as compared with the adjacent limestones. 



