18 Messrs. W. Phillips mid Kent on [Jan. 



Rocks of Grooby and its Neighbourhood. 



Considering the nature of these rocks, which appear to belong 

 to the trap family, it would have been especially desirable to 

 have perceived their connexion either with those of the forest, 

 or of Mount Sorrel, to neither of which do they seem to possess 

 any affinity ; but although we anxiously sought the junction, 

 there did not appear any opportunity of perceiving it. Owing 

 to the causes before mentioned, we did not observe any place 

 where their approach appears on the surface nearer than about 

 one-fourth of a mile, as on the north of Markfield Knowl, which 

 consists of trap. It is remarkable that when this knowl is 

 viewed from the road from Grooby to Markfield, and just before 

 it turns southwards to that place, five ridges of the trap rock are 

 perceived running down its side in the direction of the slaty 

 cleavage of the rocks of Charnwood. We mention this fact as 

 it exists, without any suspicion of its cause, or that these rocks 

 have any connexion with slates of any kind, and especially with 

 those of the forest ; the spaces between the ridges are covered 

 by a thick herbage. 



About one-fourth of a mile on the north of the lower extre- 

 mity of these ridges is a quarry beside the road from Grooby to 

 Thrinkston, and called Round Cliff Pit, in which the rocks of 

 Charnwood are broken for the purposes of the road, and which 

 here are traversed by veins of a yellowish-green substance, 

 which, from its hardness, and from the forms of some minute 

 crystals observed in crevices of the rock, we consider to be 

 epidote. The space between this quarry and the termination of 

 the ridges of trap at the foot of Markfield Knowl, is, however, 

 covered by grass, or by cultivated soil, except the small part 

 occupied by the road. 



We observed this rock but partially ; namely, on the N in 

 Bradgate Park ; thence by Grooby Pool to Grooby, and from 

 the latter place by Markfield to Markfield Knowl ; but these 

 rocks extend, according to Mr. Greenough's map, S and SW of 

 the latter place, above two miles. 



This rock consists primarily of hornblende often distinctly 

 laminated, intermixed with small masses, never exceeding the 

 size of a pea, of a reddish substance, often greatly possessing 

 the aspect of compact felspar, the fractured surfaces being com- 

 monly without lustre ; these two ingredients constitute the rock 

 in about equal proportions ; in other instances the red felspar (if 

 so it may be termed) has a distinct though not brilliant cleavage, 

 but only in one direction. With the reddish substance is often 

 associated another, either of a light or bottle-green colour, of 

 which the surfaces are more brilliant than those of the former, 

 and we succeeded in detaching several fragments, having cleav- 

 ages at least in two directions, but scarcely bright enough for 

 the use of the reflective goniometer : one of them, however, 



