1824.] the Rocks of Mount Sorrel, S)C 9 



basalt, and is sufficiently hard to admit of a flat conchoidal 

 fracture ; it yields to the knife, though not without considerable 

 pressure ; is of a dark colour, owing to the thorough intermix- 

 ture of specks of a dark-green substance, and the slender crystals 

 of felspar are innumerable ; but neither quartz nor any other 

 mineral is to be detected even by the help of a highly magnify- 

 ing glass. The rock in immediate contact with this dyke did not 

 appear to have suffered any alteration. 



The rocks of Mount Sorrel are occasionally also traversed by 

 small veins which more decidedly belong to the rock itself. 

 These veins sometimes resemble granular felspar, sometimes 

 granular quartz : they are always of a red hue : when of felspar, 

 they appear to include minute specks of quartz, hornblende, and 

 chlorite ; while those of quartz inclose crystals of quartz, felspar, 

 hornblende, and iron pyrites. The veins of white or translucent 

 quartz usually contain chlorite, and sometimes epidote. 



No appearances of regular stratification are to be observed in 

 any of the quarries of this rock ; at the western termination of 

 their line at the back of the town, however, slabs of considera- 

 ble dimension are procured, owing to the presence of nearly 

 parallel fissures in two opposite directions, both being nearly 

 vertical, and those producing the largest plane, running nearly 

 due E and W. In the quarry at the other side of the hill, and 

 due E of the windmill on its summit, are to be seen some natu-< 

 ral cleavages in various directions, which, without sufficient 

 caution, might be mistaken for dykes. 



Of the Rocks of Charnwood Forest, 



The rocks of the district of Charnwood Forest, coloured 

 yellow in the accompanying sketch, differ greatly in respect of 

 aspect and composition, and vary so greatly in their external 

 characters, that although, from the circumstances attending 

 them, it is impossible to doubt their common origin, there are 

 varieties which, if taken separately, would, without previous 

 acquaintance with them, be judged to be of very different ages, 

 since even some of the proximate rocks appear to possess as 

 little mineralogical affinity as chalk and flint. 



The greater part of these rocks are certainly schistose, but in 

 degrees varying from a fissility approaching that of common slate 

 to that of the rudest kind in which this seeming consequence of 

 structure is to be perceived; even the most completely schistose 

 varieties differ greatly in composition and external character ; 

 while those that are Least so often contain fragments of other 

 substances which, perhaps, tend to characterise the whole (since 

 all the varieties occur interstratified without any order), as belong- 

 ing to that class of rocks which are denominated by Dr. 

 Mac Culloch primitive slates ; by others grey wacke. And here 

 it may be pertinent to remark, that in no instance was any trace 

 of organic exuviee observed. 



