XIII. ] GEOGNOSY OF THE APPALACHIANS. 273 



been clearly defined by Sedgwick, who groups the rocks of 

 Skiddaw into four divisions. The lowest of these, succeeding 

 the granite, is a series of crystalline rocks, not described litho- 

 logically, with mineral veins, " having some resemblance to the 

 rocks of Cornwall," and including, towards the summit, " chi- 

 astolite-schists and chiastolite-rocks." These are followed in 

 ascending order by two great series of slates and grits, suc- 

 ceede'd by a fourth division of schists, sometimes carbonaceous, 

 holding in parts fucoids and graptolites, which are apparently 

 overlaid discordantly by sundry trappean conglomerates and 

 chloritic slates.* The graptolites of the Skiddaw slates are 

 found to be identical with those of the Levis formation,t and 

 it is worthy of notice that although Sedgwick places the mica- 

 schists with andalusite (chiastolite) so far below the graptolitic 

 beds, he elsewhere, in comparing the rocks of North Wales 

 and Cumberland, states that the chloritic and micaceous rocks 

 of Anglesea and Caernarvon are not represented in Cumber- 

 land, being distinct from the other rocks of North Wales, and 

 much older. J 



In Victoria, Australia, the position of the chiastolite schists, 

 according to Selwyn, is beneath the graptolitic slates. Boblaye, 

 it is true, asserted in 1838 that the chiastolite-schists of Les 

 Salles, near Pontivy in Brittany, include Orthis and Calymene; 

 but when we remember that even experienced observers in the 

 White Mountains for a time mistook for remains of Crustacea 

 and brachiopods, certain obscure forms, which they afterwards 

 found not to be organic, and that Dana, in this connection, has 

 called attention to the deceptive resemblance to fossils presented 

 by some imperfectly developed chiastolite crystals in the same 

 region, 1 1 we may well require a verification of Boblaye's obser- 

 vation, especially since we find that more recently D'Archiac 

 and Dalimier agree with De Beaumont and Dufrenoy in placing 



* Synopsis of British Palaeozoic Rocks, p. Ixxxiv, being an Introduction to 

 McCoy's Brit. Pal. Fossils (1855). 



t Harkness and Salter, Quar. Jour. Geol. Soc., XIX. 135. 

 J Geol. Journal (1845), IV. 583. 

 Bull. Soc. Geol. de Fr., X. 227. 

 || American Journal of Science (2), I. 415, V. 116. 



12* R 



