6 Messrs. W. Phillips and Kent on [Jan. 



first instance aware of the intermixture of these two minerals in 

 this rock, and considering the whole as felspar, we should have 

 contented ourselves with the observation that a part of it yields 

 to the pressure of the edge of the hard mineralogical knife, 

 which felspar does not, but for the discovery of M. Levy, that 

 much which has been considered as felspar is cleavelandite ; the 

 announcement of this in the Annals for November last, induced 

 us to examine all the varieties of this rock with great attention, 

 and we have been convinced of the intermixture of the two 

 minerals by procuring fragments from the same specimen ; 

 which, submitted to the reflective goniometer, afforded us sepa- 

 rately the angles of the two substances; felspar cleaves with 

 ease only in that direction which affords an angle of 90° ; while 

 cleavelandite yields with nearly equal ease parallel to all the 

 planes of its primary crystal, and we have consequently obtained 

 the measurement of all its angles. 



The Mount Sorrel rock thus constituted* will be judged by 

 some to be a syenite ; while others will consider it to be a gra- 

 nite of the compound kind described by Dr. Mac Culloch, in his 

 excellent Treatise on Rocks, under the Third Division, relating 

 to that rock (p. 238), and it is to be regretted that no sufficient 

 means of determining its actual geological position (which alone 

 might settle the question) is afforded, since it is not seen in 

 connexion with any other rock, save the beds of the new red 

 sandstone, which, as has already been stated, repose on it. 



But there are still some circumstances regard in<r this rock 

 which merit attention. It not unfrequently includes either 

 irregular or somewhat spherical masses, varying in size from 

 about an inch in diameter to nearly a foot, and possessing a totally 

 different aspect to the rock itself; some of these have at first 

 sight the appearance of fragments, but not even a close inspec- 

 tion with a glass can discover the precise line of junction with 

 the rock. Their aspect is fine-grained, and their composition 

 appears to be, minute quartz, felspar, hornblende, and chlorite, 

 apparently imbedded in a substance of a hair-brown colour, 

 which yields to the knife readily, and resembles steatite. The 

 mass partakes of a brown colour with a tinge of green, espe- 

 cially when moistened : in one instance, specks of yellow copper 

 ore and whitish pyrites were apparent ; in another, the same 

 ingredients are visible, and as effervescence is produced by the 

 application of diluted muriatic acid, it may be assumed also to 

 include calcareous spar. 



This rock also contains veins or dykes : the substances of 



* M r e must not make any particular exception of this rock, on account of its contain- 

 ing cleavelandite abundantly. This mineral has since been found entering into the com- 

 position of a porphyritic granite from Cornwall ; in the granite of Shap in Westmore- 

 land, and in a porphyry from Glen Tilt in Scotland, as announced in the slnnals for 

 December ; and still more recently in the porphyritic rocks of Charnwood Forest ; and 

 probably also in the neighbouring trap rocks of Grooby, in Leicestershire ; in each of 

 thet-e it is accompanied by felspar. 



