56 COLEMAN ON THE MICROSCOPIC 



Scapolite. — In addition to the plagioclase, aud often largely replacing it, is a mineral 

 which appeal's to be one of the scapolites. It forms irregularly shaped masses, wedged in 

 between the hornblende aud plagioclase ; or else oval portions are massed together, with 

 their longer axes nearly in the same direction. Sections not at right angles to the chief 

 axis, nor nearly so, shew a decided longitudinal cleavage, sometimes with hints of an- 

 other cleavage perpendicular to it. These sections shew bright red aud green hues in 

 polarised light, and are bordered with strips of rainbow colors. Extinction is very perfect 

 parallel to the cleaA'age. 



Other sections nearly at right angles to the chief axis have a rather imperfect rect- 

 angular cleavage or no definite cleavage at all. Such sections give faint coloration or 

 none between crossed niçois, and observed thus with the eyepiece removed, display a 

 black cross which does not separate into hyperbolas on revolution. The mineral is quad- 

 ratic and optically negative. The only specimens that could be examined macroscop- 

 ically were from a veinlike portion of rather weathered rock. They have a yellowish 

 color, waxy lustre, aud hardness of about three. A portion examined by blowpipe 

 methods by Dr. Haauel was pronounced " wilsonite ", a modified scapolite. A less 

 weathered portion obtained \\\i\\ difficulty gave hardly a trace of moisture iu the matrass ; 

 so that probably the clear sections observed under the microscope may be considered 

 scapolite (Plate I, fig. 4). 



In most sections, the mineral appears quite fresh and free from inclusions. The plagio- 

 clase beside it is of the ordinary type and but little weathered, so that the scapolite must 

 be considered an original constituent of the rock. Since it makes up in most cases at 

 least a quarter of the whole (as estimated under the microscope), it canuot be looked on 

 as an accessory mineral. 



Magnetite is common in the rock, while ilmenite and titanite are much less so. A 

 little cjuartz occurs in perhaps half the sections, and orthoclase is suspected in a few. 

 Biotite is seen now and then, but in very small quantities. The rock, which is not un- 

 common in the drift, may be named : — 



Scapolite-dionte-schist, or possibly, since the schistose character is rather undecided, it 

 may prove to be scapolite-diorite. 



One specimen proved on examination to contain beside much hornblende and scapolite, 

 a considerable amount of microcline and quartz, the latter with fluid inclusions and 

 moving bubbles. In addition to the minerals mentioned, a large quantity of sea-green 

 angite was found, often bordered with hornblende, the two minerals having their chief 

 axis in common. This rock seems to connect scapolite-diorite-schist with gneiss on the 

 one hand, and diabase on the other, certainly a wide range of affinities. 



Diorite and Hornblendic Schists. 



Coming now to the undoubtedly schistose hornblendic rocks we find a most extensive 

 aud varied, but not specially interesting, group of rocks. They fill the same position in 

 reference to the diorites as the gneisses occupy toward the granites. They range from 

 compact to coarse grained. In color they are chiefly dark grey, verging on green. In 

 structure they are usually distinctly schistose, sometimes exceedingly so, the cleaA'^age 

 being determined by the parallelism of the hornblende individuals. In some cases where 



