DALY: GEOLOGY OF THE NORTHEAST COAST OF LABRADOR. 221 



part of the thousand-foot cliff is made up, as they are, of a volcanic breccia. 

 The basalt agglomerate, which is also a significant part of the stratified 

 series, is typical and encloses numerous bombs with bread-crust structure. 



These sediments and intercalated traps everywhere have low dips ; 

 therein we have an explanation of the plateau-like character of the 

 relief, as dissimilar to any other on the coast, as the residuals of Tor- 

 ridonian sandstone are unlike the rolls of gneiss in the Scottish High- 

 lands. Combining the observations made in the gorge below the waterfall, 

 with those made in the Tickle and outside to the southeast of the Bishop's 

 Mitre, the structure of the rocks on the northwest side of the Tickle is 

 that of a flat syncline with a N. W.-S.E. axis, crossed, west of the water- 

 fall, by a transverse warp. On the southwest, the effect is that of an 

 eroded low half-dome. The steepest dips occur near the middle of the 

 Tickle, where a magnificent section of the whole stratified series can be 

 easily studied as the beds plunge into the deep water (Plate l). The 

 total thickness of the stratified series is about twenty-five hundred feet. 



On Ogua'lik at the southwest end of the Tickle, the gneisses are over- 

 lain by an intrusive sheet of diabase, about fifty feet in thickness, upon 

 wdiich are piled slates, quartzites, limestones, and sandstones with inter- 

 bedded traps. Whether the latter are intrusive or extrusive we had not 

 time to determine, but the apparently complete absence of vesicular 

 structure and of other signs of volcanic activity would speak for the 

 latter interpretation. The limestone is rather crystalline, and is sti'ongly 

 charged with pyrite. A shallow opening and a few rusty tools showed 

 that attempts had been made to test the rock for either gold or copper. 



The whole of Ogua'lik corresponds in composition with these cliffs of 

 the northwestern shore of the island. At the eastern end, black cliffs, 

 fifteen hundred feet in height, form the edges of a capping massive sheet 

 of trap estimated at seven hundred feet in thickness, overlying some nine 

 hundred feet of sediments again unconformable on the gneissic complex. 

 While there exists a general similarity between the formations on either 

 side of Mugford Tickle, their failure to match on opposite sides of the 

 strait seems to imply a fault coincident with it in direction. 



The unconformity of the crystalline basement and the sediments is 

 extremely well shown at both ends of the Tickle, especially at Cape 

 Mugford itself (Plate 2). The gneisses have participated in the fold- 

 ing of the sedimentary cover ; it is owing to that fact that they disap- 

 pear in the middle cliffs of the strait. The surface of unconformity 

 would, if produced, rise to seaward so as to pass completely over the 

 fantastic peaks of Nanuktut Island. This island thus forms a strangely 



