PRECAKBONIEEROTJS ROCKS OF CHARNWOOD FOREST. 237 



ring the Charnwood series, also, to the same remote period than 

 there has hitherto been, the arguments previously advanced in 

 favour of this (except as regards their strike *) being wholly unten- 

 able. At present the case must be regarded as sub judice. If the 

 verdict can ever be given, and it is for Precambrian, then the 

 Charnwood rocks will probably correspond with the Pebidian series 

 of Mr. Hicks. 



Age of the Igneous Rocks. 



If the age of the stratified rocks is uncertain, much more is that 

 of the igneous rocks intruded into them. Let us, however, assume 

 that the former are on the horizon of the Borrowdale series, and 

 see if we can then attempt an approximation. 



The Southern Syenites, as we have stated, are probably intruded 

 among rocks rather high up in the group. The Groby rock (and 

 we may say this of all in that district), according to Mr. Sorby, 

 solidified at a great depth, certainly not less than several thousand 

 feet. No Upper Silurian has been discovered nearer to Charnwood 

 than the northern part of the South-Staffordshire coal-field f; and, 

 so far as we can make any assumption with regard to the rocks of 

 this period, we should infer that the series would hardly be so thick 

 as it is in the Lake district. Hence we cannot suppose the 

 syenite to have been intruded before the end of the Upper Silurian 

 period. Now, having regard to the general configuration of the 

 Forest, it is in the highest degree probable that much denudation 

 had taken place before Lower Carboniferous rocks were deposited. 

 The granites of the Lake district are intrusive in the Skiddaw 

 Slate, Borrowdale series, and Coniston Flags (at Shap), and solidi- 

 fied at great depths %. There can be no doubt that at any rate the 

 Shap Granite must have been intruded about the time when depo- 

 sition ceased and denudation and upheaval commenced — that is, 

 about the commencement of the Old Eed Sandstone period. Analogy, 

 then, leads us to assign the same period for the Charnwood syenites. 

 The correspondence of the strike in this district with that of the 

 Borrowdale series, near Ingleton, suggests that the two lie on an 

 area acted on by the same forces. We can hardly assign a later 

 date to the hornblendic granite of Mount Sorrel ; but, beyond the 

 fact that it is almost certainly an intrusion in the gneiss §, of the age 

 of which we are ignorant, nothing can be said. We may, however, 



* Attention was called to this as suggesting a Precambrian age by Dr. Holl 

 and others. See Woodward, ' Geology of England and Wales,' p. 24. 



t Pierced in coal-sinkings near Cannock, and probably underlying all the 

 coal-field to the north. 



\ According to Mr. Ward (Q. J. G. S. vol. xxxi. p. 589) the Shap Granite 

 was consolidated at a maximum depth of 14,000 feet. 



§ The extremely altered condition of this (which seems more than can be 

 satisfactorily explained in this district by the proximity of the granite) suggests 

 that it may possibly be a solitary fragment of a group earlier than that of the 

 Forest rocks. There is some reason to think that the Malvern ridge exhibits 

 Precambrian rocks of two ages. 



