DALY: GEOLOGY OF THE NORTHEAST COAST OF LABRADOR. 213 
the almost universal covering of peat, to a grayish-white color highly 
suggestive of weathered quartzite. The structure is linear-parallel and 
is formed with extraordinary perfection. The gneiss is penetrated by 
dikes and more irregular intrusions of diorite which are probably related 
as to age and origin with the trappean mass of Tub Island. 
Nowhere on this coast are trap-dikes so massive or so influential in 
determining the topographic form of the country, as in the region about 
Ice Tickle on the north side of Hamilton Inlet. Rodney Mundy Island 
and Ice Tickle Island are each about three parts composed of medium 
to coarse grained hornblende granitite, granitoid gneiss and fine-grained 
gneisses. The remaining surface is occupied by a multitude of great 
dikes, thick sheets, pods, or stock-like bodies of diabase which, on 
account of their black color, contrast very strongly with the other crys- 
tallines round about. The trap wherever examined is plainly intrusive. 
No vesicular structure was to be found. Both contacts of a typical pod 
showed the chilled and porphyritic zone characteristic of intrusion. A 
fine example of the dikes is seen on the ridge at Indian Harbor. It has 
parallel walls, is some two hundred feet in width, and is visible as a steep 
black wall a quarter of a mile along the Tickle. Very commonly the 
dikes are seen to swell out into thick trap-bodies three hundred to one 
thousand feet in diameter, and again, a stock will project through the 
gneisses without visible connection with the trap of the neighboring 
hills. The average strike of the intrusive masses is N. E.-S. W. The 
trap forms all the higher elevations, which thus assume the varying out- 
lines of palisade, ridge, or dome, according to the shape of the intruded 
rock-body. Between them the schists and granites, on account of their 
inferior power to resist erosion, now underlie valleys that open sea- 
ward on the deep bays and tickles of a “drowned” coast-line. One will 
go far to discover so fine an example among wholly crystalline rocks, of 
such control over land-forms— the control of differential resistance to 
weathering. 
The same association of gneiss-valleys and trap-hills extends at least 
ten miles to the westward of Ice Tickle. At Sloop Harbor, though still 
plentiful, the dikes (here hornblende biotite diorite with accessory augite) 
are too narrow to produce a great effect on the topography. Webeck 
Island, a soilless, driftless, because wave-swept, granitic swell a half-mile 
or more in length, affords a splendid exhibition of twenty-two huge 
dikes cutting across the island in parallel fashion. On the mainland, 
opposite Jigger Island near Webeck Island, an intéresting group of dikes 
in granitite was studied. One of these is a handsome biotite diorite 
