244 JOURNAL OF THE PLYMOUTH INSTITUTION. 
spotty, the spots being of an oblong or oval form, and a few 
crystals of chiastolite appear. ‘Then these crystals become more 
numerous, so as to entitle the rock to the name of chiastolite-slate. 
This passes into a harder, more thickly-bedded, foliated, or massive 
rock—spotted- (or andalusite-) schist; and this again into mica- 
schist, of a generally grey or brown colour, and occurring immedi- 
ately around the granite.” 
Ivybridge is the only place in this neighbourhood where 
chiastolite-slate is well developed ; and there it fully answers Mr. 
Ward’s description, the colour being bluish-black, and the slender 
brownish-white —they are hardly the pale yellowish-white of 
Skiddaw—crystals of chiastolite sometimes more than half an 
inch in length. Microscopic examination shows very clearly the 
peculiar structure whence this mineral derives its name—transverse 
‘‘cross” markings, due to the presence of foreign matter in a 
granular form. This is rarely visible locally to the naked eye. 
The gradual alteration in the normal condition of the slates as 
they approach the granite, is best seen in the vicinity of Shaugh 
and Meavy. ‘The first step is the development of a slightly 
unctuous or of a silky character, passing on, in the one case, into 
talcose-slate, or, in the other, into the spotted andalusite-slate 
already noticed. 
The silky schist is best noted at Shaugh. It has a very fine, 
fibrous, glossy, texture, with a sericitic aspect. The microscope 
reveals the existence of bladed crystals in beautiful radiating 
groups, and of little colourless microliths. 
The spotted or andalusite-slates form the great bulk of the 
altered rocks. The andalusite is commonly nodular, and _ its 
approach to crystalline forms is very imperfect ; though crystalline 
structure is apparent in many instances on careful examination, 
expecially with the microscope. Andalusite is best developed near 
Cornwood, where the particles are larger, and more thickly scattered 
through the rock, than elsewhere. Here also the largest crystals of 
chiastolite in the neighbourhood are to be found, though there is 
no such distinct occurrence of chiastolite-rock as at Ivybridge. 
The passage from the andalusite-slates into the mica-schist next 
the granite is apparently made by the development of mica in the 
andalusite nodules. The rock gradually becomes spotted with 
glittering mica instead of with the dull andalusite, and these spots 
increase and spread until they form layers, and we have a 
