No. 8. — Contributions from the PctrograijJiical Laboratory of the 

 Harvard University Museum. 



II. 



On some Occurreiices of Ottrelite and Ilmenite Schist in Neio England. 



By J. E. Wolff. 



In the sei'ies of metamorphosed sediments which, in the many locali- 

 ties, represent nearly every geological horizon, a wide-spread type of rocks 

 are characterized by their fine grain, glistening micaceous aspect, and 

 perfection of cleavage, to which the names of phyllite, micaceous slate, 

 argillaceous mica schist, etc. have been applied. They represent 

 original fine-grained argillaceous sediments, in which the metamorphic 

 development of new minerals combined with the production of cleavage 

 has partially or totally changed the original character. These rocks 

 frequently attract attention by the presence of porphyritic, more or less 

 perfectly shaped crystals, scattered through the fine-grained micaceous 

 paste, which, unlike the analogous crystals of porphyritic eruptive rocks, 

 appear to have formed later than the " groundmass." Garnet, biotite, 

 andalusite (chiastolite), staurolite, albite, magnetite, ilmenite, and min- 

 erals of the ottrelite group, occur in this w^ay. In this paper some 

 notes are presented on schists or phyllites containing ottrelite or 

 ilmenite plates. 



Ottrelite or chloritoid schists of Archean, Cambrian, Carboniferous, 

 and perhaps of later age, have been described from numerous localities 

 in Europe. The Cambrian phyllites of the Ardennes, among which the 

 classical ottrelite schists occur, have undergone a thorough chemical and 

 mici'oscopical investigation by M. Renard.-' One of these rocks is of par- 

 ticular interest in this connection, namely, the " Phyllade a ilmenite des 

 Forges de la Commune." The bluish gray rock contains numerous small 

 glittering metallic plates which can easily be mistaken for ottrelite ; in 

 the section they are transparent on the thin edge, with a brown color, 



1 Hull. Mus. i;. Hist. Nat. Boly., Vol I pp. 212-'21'.). V(,l TI. pp 127-152, 



\'.il. III. pp. 81, s.'>, •j:;0-2(!H 



vOL. XVI. — NO. b 



