Classification of Massive. Rocks. 213 
(b 1) sahlite diabase, which contains an, idiomorphic 
colorless monoclinic pyroxene (sahlite), and 
(6 2) enstatite diabase, containing an orthorhombic 
augite. 
(C) teschenite is analcite-bearing. 
2. OLIVINE D1aBasEs contain olivine as an essential constituent 
in addition to plagioclase and augite. 
G. THE THERALITES. 
The theralites, formerly called teschenites, are intended to embrace 
rocks composed of. plagioclase and nepheline, together with the 
accessories angite, biotite and olivine. Rocks of this composition 
are not known to exist among the intrusives, unless certain basic 
rocks from Montana, lately described by Mr. Wolff, belong here. 
Corresponding members of the effusive class are, however, quite 
well known, and it is therefore expected that true theralites will be 
found at some time in the future, even if the Montana rocks should 
turn out not to belong in this family. 
H. THE PERIDOTITES. 
The peridotites are the most basic of the intrusive rocks. They 
contain no plagioclase, but usually do contain a large amount of 
olivine and a mineral of the amphibole or pyroxene families. Their 
bisilicate constituent is made use of for purposes of sub-classifi- 
cation. 
1. Prcrrre is composed of olivine and augite. 
2. ÅMPHIBOLE Prcrrre contains olivine and hornblende. 
3. WEHRLITE consists of olivine and diallage. 
4. HARZBURGITE is a combination of olivine and a rhombic 
pyroxene. : 
5. LHERZOLITE contains olivine, diallage and a rhombic pyroxene. 
6. Dursrre consists of olivine and chromite. 
II. Vern Rocks. 
The class of vein rocks includes those which exist as independent 
geological bodies only in the form of veins or dykes, although many 
similar rocks occur also as facies of certain intrusive and effusive 
rocks. This class is not as well defined as either the intrusive or 
the effusive class, Rosenbusch personally is inclined to place them 
