378 On the Geological Structure 



some of the specimens above mentioned from Douce, I have 

 ascertained the identity of Karstcn's mineral with Anda- 

 liisitc. I have not found however, that his claim to the 

 first detection of this species has been mentioned by subse- 

 quent writers; although his opinion with respect to its 

 affinity with felspar, accords with that which Haiiy is dis- 

 posed from his latest observations to adopt: Tableau coni' 

 pararif, 8:c, p. 217. 



To the Andalusite is also to be referred, a mineral which 

 occurs in great abundance at Killincy in the county of 

 Dublin, first observed there by Dr. Blake, and for some 

 time considered as belonging to a species not described by 

 mineralogists : the schist at the southern extremity of the 

 Scalp, appears to contain (he same substance, as well as 

 that next to be described ; and it is fouhd also near the 

 head of Glenmacanass. It is most remarkable on the shore 

 at Killbiey, at the southern extremity of the cliff under the 

 obelisk hill, where it abounds on the surface of the mica- 

 slate, and also imbedded in the rock. In a recent fracture, 

 it is imperfectly distinguishable from the mass of the stone; 

 but as it resists decomposition better than the other sub- 

 stances of which the aggregate is composed, it appears very 

 distinctly on the surfaces which have been long exposed to 

 the weather. 



The Andaluslte when thus brought to view, appeors ge- 

 nerally in the form of embossed groups, consisting of slen- 

 der prismatic crystalline shoots, of a dull greyish black 

 colour, which are sometimes assembled in a stellated form, 

 but more frequently without any determinate arrangement: 

 these .ire commonly rf)unded at the edges from the effects 

 of decomposition, and in that case, several of their principal 

 characters are scarcely to be distinguished ; but in the 

 pieces least affected by exposure, when attentively examined, 

 the crvstalline form, colour, lustre, cleavage, and other 

 characters of this species, are sufficiently distinct. 



5. The andalusite of Douce-mountain is accompanied, 

 as has been mentioned, by another mineral besides quartz 

 and mica ; the characters of which have much affinity to 

 those of the iiulurated talc of Werner, and which is placed 

 iinder that denomination in the collection of Dublin Col- 

 lege (Nos. 495 — 6 — 7) : a specimen of the same kind, 

 stated to be Irom Glendulogh, in the county of Wicklow, 

 was found also m that collection (No. 40-t) ; and a similar 

 substance was observed by Mr. Stephens at the southern 

 extremity of the Scalp. 



The following are some of the characters exhibited by 



the 



