156 MINERALOGY AND ‘LITHOLOGY. 
Pl. 5 in Fig. 3. The rock contains augite of a light pink color, much 
green chlorite, and a little biotite. The iron oxide is titanic iron, and 
its solid centres are usually surrounded by a gray, translucent rim. Apa- 
tite is abundant. 
The massive portion of this rock has been analyzéd by Mr. Pease, of 
the Sheffield laboratory, with the following result: 
Silica, ‘ ‘ a . r 2 ‘ a . g - 47.38 
Alumina, és s ° s é . 5 ‘ - F é 19.08 
Tron sesquioxide, . ‘ _ . a ‘. * < ‘ : 2.66 
Iron protoxide, : ‘ , 5 ’ . 3 a A ‘i 8.81 
Lime, . ‘ : : . 5 2 - , 2 F : 8.37 
Magnesia, 5 . . : . 7 ‘ c 4 . 5 6.07 
Soda, : : : . 3 ‘i 5 3 A 5 ‘ ‘ 3-54 
Potash, . 3 ; 3 z ‘ 2 . 3 o 6 F 1.31 
Water, . . * ‘ ‘ a E : ‘ 7 . 3-39 
Carbonicacid,. . . @ : ‘ i ‘ c - 5 79 
101.40 
Specific gravity, 2.go. 
An analysis of the anorthite from this rock has been given on page 91, 
which indicated the ‘composition of the aggregate into which the large 
crystals have been converted. But the feldspar in the compact part of 
the rock is not so altered as are the large anorthite crystals; and the 
analysis points towards a soda lime feldspar like labradorite, and makes 
it probable that two kinds of triclinic feldspars are present, as has often 
been proved to be the case elsewhere. 
A specimen from Moose Mountain, and another from Stark, offer no 
further peculiarities, save the presence ih them of much pyrites. A 
specimen from Concord, Vt., contains much calcite, and 'the anorthite is 
almost entirely altered into ‘an aggregate. 
Besides the occurrences of diabase porphyries that have been men- 
tioned, there are a great many others in which the feldspar has reached 
such a state of decomposition that neithér analysis nor the microscope 
can determine its species. In regard ‘to all these, it may be said, that 
whether originally labradorite or anorthite is ‘now of little consequen¢e, 
since time has reduced one and the other to the same thing, and for such 
rocks porphyritic diabase is a name sufficiently satisfactory. It may ‘be 
