44 DESCRIPTION OF THE PRIMARY [CJh. IV. 



on the side of the hills in blocks three or four feet in breadth : 

 its hornblende gradually loses its characters, until at length 

 it cannot be recognised as such, having passed into shorl, and 

 thus the transition is effected into proteolite, the genus last 

 described. 



In like manner, proceeding over the greenstone in a con- 

 trary direction, towards the shores of Mount's Bay, the acces- 

 sary mineral, hornblende, becomes gradually changed into 

 actynolite, as is evident in those rocks which have a compact 

 and crystalline structure. This genus is not of very common 

 occurrence, and may therefore be noticed a little more in 

 detail. 



The most abundant species of actynolite-rock is hard and 

 compact, known provincially by the names of blue-stone or 

 blue elvan. This variety is accompanied by, and gradually 

 passes into a blue slate, which is fissile in various degrees, 

 and may also be easily separated into small rhomboidal pieces. 

 The massive kind occurs in elevated ridges on the coast, and 

 is very durable, whilst the slate is decayed to a considerable 

 depth, still retaining its form, but progressively diminishing 

 in tenacity from the perfect rock to the surface, where it is 

 sometimes nearly as soft as clay : the blue colour of the slate 

 has disappeared in the decomposed rock, which is ash- white, 

 with ochreous stains, or of an uniform pale fawn colour ; this 

 property readily distinguishes it from slaty greenstone, with 

 which it is nearly allied. Some of the compact kinds of this 

 genus are very beautiful, having a light violet-coloured basis, 

 which is variegated with stripes, and marbled markings of the 

 dark blue species. The violet colour appears to be occasioned 

 by the intimate union of axinite with the compact felspar 

 basis of this rock ; for axinite, in crystals, is often present, in 

 the state of patches and small veins, traversing the rock after 

 the manner of calcareous spar in limestone. At first sight, 

 these rocks appear to be well calculated for ornamental pur- 

 poses, but unfortunately they are traversed by numerous 

 seams or joints, which become discoloured by exposure to the 



