PRECARBO^IFEROUS ROCKS OF CHARNWOOD FOREST. 789 



We shall also discuss at greater length the microscopic structure of 

 the rocks, both sedimentary and igneous, and offer some remarks 

 upon the comparative lithology of the former and upon their probable 

 geological age, which Mr. Bonney has already stated to be, in his 

 opinion, not Cambrian (Survey), but about that of the Borrowdale 

 series of the Lake district. 



The authors desire to express their thanks to A. M. P. De Lisle, 

 Esq., Mrs. Perry-Herrick, Alfred Ellis, Esq., and other owners of 

 property, who have most kindly allowed them free access to every 

 place, and to the owners and managers of the various quarries for 

 similar facilities. They have also to thank A. Hill, Esq., of Cooper's- 

 Hill College, for assistance in the field-work. 



Discussion. 



Prof. Ramsay said that though it was many years since he saw 

 the country described in this paper, and twenty years since it was 

 mapped, he and the officers of the Survey, who did the work,, were 

 quite convinced that a proportion of the so-called igneous rocks were 

 only igneous in the sense of extreme metamorphism. 



Rev. T. G. Bonxey said that in this district in most cases the 

 metamorphism was not extreme. There is no porphyry ; and much 

 of the felspar which is present porphyritically is detrital. 



Mr. Hicks was surprised to find so great a resemblance between 

 the rock specimens now exhibited and those he had recently brought 

 before the Society from the pre-Cambrian rocks of St. David's. He 

 would draw particular attention to the conglomerate shown, as it 

 contained distinct pebbles of schists and indurated shales, derived 

 primarily from rocks in a state of metamorphism. That these 

 pebbles were in this state previous to being cemented together to 

 form the conglomerate was clear from the fact that the pebbles still 

 retain their distinct outline ; and the matrix is not apparently much 

 altered. It is clear also that these masses could not have been derived 

 from the Cambrian or Lower Silurian rocks, as all evidence so far 

 obtained in regard to the physical conditions of the Cambrian and 

 Lower- Silurian epochs in Western Europe goes to show that these 

 rocks were not elevated out of the horizontal position until the close 

 of the Lower-Silurian, and hence that they could not have been pre- 

 viously indurated sufficiently to yield pebbles of this nature. He 

 felt convinced that some at least of these rocks would prove to be of 

 pre-Cambrian age, and would have to be correlated with those he 

 had recently described under the names " Dimetian " and " Pebi- 

 dian." 



Prof. Ramsay altogether denied the absence of pebbles in the 

 rocks referred to by Mr. Hicks. There were plenty of them, both 

 of Cambrian and of Silurian age. 



that these are also intrusive in slaty rock, "which doubtless belongs to the 

 Forest series. 



Q.J.G.S. No. 132. 3f 



