of the Malvern Wills, 97 



ih a direction nearly at right angles. Wherever I coiUd examine it, it wc.i 

 so weathered as to render my decisions very fallacious. It has, however, to 

 Jill appearances a decomposed basis of felspar (clay -slate) with folia of mica, to- 

 wards tlie surface, and, when exj)osed to decomposing agents, (Mssessiiig a high 

 metalline lustre, becoming towards the centre of the rock, dark and shining. 

 If the formation was sufficiently extensive, it would be called a porjjhyry. I 

 have only met with an account of a similar rock occurring near Felsobanya in 

 Transylvania, and in Saxony. With respect to the accuracy of denominating 

 these formations Sienite, 1 need only remark, tliat, notwithstanding it has 

 been proved that the rock from which a supposed similar series has received 

 its name from the time of Pliny, is not a compound of hornblende, quartz 

 and felspar, as first advanced by Werner, and that this name becomes no 

 longer applicable to the same set *, still, under all circumstances, this rock 

 has no claim to that title : the dissemination of hornblende is not universal, 

 though in some places abundant, yet it is regulated by particular localities. 

 The existence of mica, in some places so abundant, is at once decisive as to 

 its real characters ; and though hornblende is met with as a mineral occur- 

 ring often in abundance, but yet not so universally as to be entitled to be 

 called a mineral constituent, or to give to the formation a name depending 

 on its occurrence. 



Under these circumstances, Worcestershire Beacon and North Hill, like 

 Hereford Beacon, will be formed of granite, containing occasionally crystals 

 of hornblende, and associated with gneiss, which, with little variation, forms 

 the northern part of the Beacon, and the whole of the North Hill. I did not 

 perceive it any where alternating with the granite* 



To the north, then, the central granite varies slightly in its appearance, 

 becoming slaty -granular, yet scarcely ever losing its distinctive characters. 

 Towards the south, however, it presents more remarkable differences, and be- 

 comes scarcely recognisable in the more compact and less crystalhne rocks 

 forming the southern outline of the mountain-range. On the hill to the 

 south of Hereford Beacon, a cave has been artificially hewn out of a portion 

 of the mountain rock, which juts out beyond the regular acclivity, bar- 

 ren, and covered only with a few stunted lichens. In this cave, though 

 not many feet deep, the Hypnum splendens and luiescens, and a Bryitm^ ])ut 

 forth their leaves to a vegetation never exceeding five or six lines in length, 

 and then wither. This portion of the rock is more compact than the body 

 of the hill, and proves that the nature of the mountain must not be judged 

 of by the examination of a portion which, by the opposition its structure of- 

 fers to decomposing agents, is barren, and unclothed with vegetation, offering, 



same time, by the increase in size thus given to its particles, disseminateti so generally through the 

 mass, uniting chemically and mechanically to destroy the cohesion, and Influence the further de- 

 composition of the rock Itself. In a close-grained granite, the felspar becomes of a redder hue, and k 

 gradually reduced to an impalpable powder, or from the quantity of alumina entering Into its com- 

 position, forms a basis of slate-clay : the pieces of quartz change gradually their form, and gene- 

 rally roll off in the shape of pebbles ; while the lamella: of mica, the last to be decoropoted, oftm 

 t-xhibit a metalline lustre. 



• M. de Humboldt has proposed the name of Sinaite. 

 OCTOBER-i— DECEMBER 1827. G 



