96 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
them. This dike crosses the road in a direction N. 70° E. (magnetic) 
having a width at the road of 23 meters (75 feet). The sandstones 
on the north side of the dike strike north-south (magnetic) and dip 
ca. 5° west. The sandstone on the south side of the dike strikes 
N. 23° W. (magnetic) and dips 7° west. West of the road the dike is 
traceable by means of small weather-boulders in a brook for about 1,098 
meters (3,600 ft.) but the trace of the dike to the east of the road was 
not followed. (See Plate 18.) 
In the disintegrated rock of the dike ose are crystals as large as a 
hen’s egg of a now rusty black augite and large flakes of a black mica 
carrying holes from which some included mineral of earlier genesis 
has been dissolved out. A soft, white, partly altered, mica is probably 
bleached biotite. The feldspar constituent was not observed. 
The most striking feature of this dike is the large number of in- 
clusions of foreign rocks which it contains. These constitute at the 
exposure in the road quite one half of the volume of the dike and 
comprise at least the following varieties of older rocks, viz: — 
Red sandy shale in fragments up to 51 em. (20 inches) diameter. 
Red shale; also a black shale. 
Coarse grained basalt with lathe-shaped feldspars. 
Fine grained basic rock. 
Amygdaloidal basalt. 
Greyish amygdaloidal basalt, less vesicular lava than the preceding. 
A fine-grained, dark, thin-laminated rock weathering white, origin 
not determined. 
The fragments of sedimentary rock may well be regarded as dis- 
rupted from the walls of the fissure which appears to have been the 
locus of a vertical displacement of the strata. Presumably the 
fragments came from underlying strata though they may just as well 
have fallen in from above. The vesicular lavas of different types, 
unless there are flows buried beneath the Lages area of sandstones, 
contrary to my own determinations of the geological structure and 
those of Dr. I. C. White, must have been derived from overlying lavas 
Though rarely, amygdales form vertical bands in dikes, they are 
characteristic of lava-flows or of lava which has been raised to the 
vent of a volcanic conduit. This dike apparently communicated in 
its time with the surface and permitted lavas already extravasated 
and cooled to yield fragments which sank in the still fluid magma of 
the dike. So much of the history which appears in the nature of the 
phenomena leads to the further conclusion that the dike communicated 
at the time of the infalling fragments with the Corisco, or some yet 
