FINE-GRAINED BASIC ROCKS. 61 
Tabulation of observations on anorthite-rock—Continued. 
Angle between 
maximum ex- 
| tinctions of 
adjacent hemi- 
’ tropic bands of 
B J the plagioclase 
2 Place | Macroscopic char-| Constituents as determined by in sections cut 
g : =I acters. microscope. at random in 
a 5 5 the zone O: ii. 
A a et 
5 eden todo) lees Angle on| 2 . 
a = = a opposite | = 
® 3 o| 5 a | sides of| 43 
a SC lala! w& | cross-hair.| = 
| 
| 
° ° ° 
803....| North shore Lake | NE.| 12 | 55 | 8W.| Rather coars e; | Anorthite makes almost the en-| 22 26 48 
Superior; Bea- nearly colorless; tire section; rare and small | 27 31 58 
ver Bay, Min- translucent. augite particles lie between | 24 28 52 
nesota. the grains of feldspar. 32 33 65 
811....) Island off south | SE.| 12 | 55 | sw.) Coarse-grained; | Anorthite, with numerous min-| 34 46 80 
Beaver Bay dark-gray. ute cavities and particles like | 31 42 73 
Point, Minne- those of No. 795, but much | 30 37 67 
sota. | smaller, makes most of the 
section. A few small augite 
particles, often altered to a 
greenish substance, lie be- 
tween the feldspars. 
822....| North shore Lake | NE.| 6| 55/ 7W.| Coars e-grained; | Pure anorthite................-. 31 33 64 
Superior; 2 | colorless to 30 43 73 
miles below white. 
BeaverBay, 
Minnesota. 
FINE-GRAINED BASIC ROCKS. 
Looking over the Keweenaw Series as a whole, the fine-grained basic 
rocks are found to prevail in extent of surface spread and total thickness over 
the coarser kinds above described, though these latter are very frequently 
met with, and constitute great thicknesses, especially in the lower portions 
of the series. Coarse-grained layers continue to quite high horizons, as, for 
instance, some of the beds of the Greenstone Group of Keweenaw Point, 
but they are here much less frequent than in the lower portions, from 
which, however, the finer-grained kinds are never absent. 
Olivine-free diabase of the ‘ ordinary type.”—In his descriptions of the 
Keweenaw Point diabases, Pumpelly recognized two types, to which he 
gave the names, respectively, of “ordinary” and “ashbed” types. ‘Che 
former name applies to the fact that, so far as his acquaintance with the 
Keweenaw Series went, that type was the most common and characteristic 
of all its crystalline rocks. The latter name was given because the type to 
