238 E. HILL AND T. G. BONNET ON TELE 



venture to assert that a great mass of rock must have been removed 

 from above it, and that, probably, in Precarboniferous times. The 

 difference between this and the Groby rock is not sufficient to 

 forbid us to assign them to the same igneous series. 



With regard to the dykes, we may be almost certain that they 

 are earlier than the Keuper, and were not intruded into deep-seated 

 rocks. We should not therefore (though we have admitted them 

 into this paper) regard them as Precarboniferous. Now at the 

 Whitwick Colliery there is, between the Coal-measures and the 

 Trias, a sheet of dolerite*, which has also been struck at Snibston, 

 and the same rock has recently been pierced at Ellis-Town Colliery, 

 one mile north of Bagworth station, the former two miles from the 

 Whitwick pit, the latter about three. Further, there are frequent 

 dykes of diorite in the Warwickshire coal-field, intrusive in Mill- 

 stone Grit and Lower Coal-measures. 



These greenstones of the Forest may, then, be of the same age as 

 the Whitwick rock, and belong to that widespread igneous action 

 which occurred in the lengthy period, not without its analogies to 

 the Old Red Sandstone, which intervened between the end of the 

 Coal-measures and the beginning of the Keuperf . 



EXPLANATION OF PLATE X. 



Map to illustrate the Precarboniferous Rocks of Charnwood Forest, Leicester- 

 shire. 



Discussion 



Prof. Ramsay said that this paper was one of great interest. In 

 the da}^s when the district under consideration was mapped by the 

 Geological Survey the microscope had not been brought into use in 

 geological work, and we are much obliged by the corrections it has 

 effected in the broad nomenclature given to us by Sir Henry de la 

 Beche. Of the masses down south, our greenstones were all dark- 

 coloured rocks, in which felspar, and especially hornblende, pre- 

 dominated ; where felspar and silica predominated they were re- 

 garded as syenites. With regard to the rocks of Charnwood Forest, 

 after much thought, there being no evidence from fossils, the officers 

 of the Geological Survey had come to the conclusion that they were 

 probably of Cambrian age. The occurrence of Precambrian rocks in 

 North Wales was spoken of in the paper as an established fact. He 

 regretted that Prof. Bonney should be of this opinion ; for all the 

 evidence was entirely opposed to such an opinion. He maintained 

 stoutly that there is an unconformity between the Lower Silurian 

 and Cambrian. Last summer he went to Ireland, and saw it there 



* See Airport, Q. J. G. S. vol. xxx p. 550. 



t The toadstones (basalts) of Derbyshire, however, show that submarine 

 volcanoes existed to the north of the Forest at a rather earlier period. 



