OLDER MORAINES OF ROSS ISLAND 263 



On the other hand, the erratics, foreign to Ross Island, of granite, gneiss, mica 

 schist, quartzite, quartz- and fels^mr-porphyry, are mostly in the form of small round 

 pebbles, just like water-worn pebbles, from an inch up to about 6 inches in diameter. 

 Occasionally one meets with larger blocks, chiefly of granite, up to from 3 to 5 tons 

 in weight. These are usually intensely smoothed, and in some cases exhibit grooving 

 on their under surfaces. 



This was noticeably the case just north of Backdoor Bay, Cape Royds. Granite 

 eri'atics could be seen there, close to Flagstaft' Point, at depths of 10 to 20 feet below 

 sea-level ; the intense rounding which the granite blocks at these lower levels had 

 undergone suggests that they had been pushed along for a considerable distance 

 under the old ice-sheet. 



Frost-weathering is so potent at Cape Royds that one never sees striae on the 

 upper surfaces of any of the boulders, as the original glaciated surface has been 

 completely splintered off. Nevertheless if the boulders be turned over and their 

 under surfaces examined, in many cases they exhibit well-marked strise, as 

 shown on Plate LXXXVI. 



We observed that at about 1350 feet (412 metres) above sea-level, about 2 

 miles east of Cape Royds, the surfiice of the kenyte of Mount Erebus appeared to be 

 grooved by glacier ice which had moved from about E.S.E. to W.N. W., evidently 

 an ancient local glacier descending from Mount Erebus. 



It is probable that much of this hummocky morame stranded along the western 

 slo^ies of Erebus rests in places upon an ice foundation. One of us (R. E. Priestley) 

 found that the upthrust marine muds near Cape Barne rested on an old foundation 

 of glacier ice, evidently an actual relic of the ice of the former Ross Barrier. Feri-ar 

 has commented on the fact that durmg the summer thaw so much thaw-water flows 

 from under these morames, that it can only be accounted for on the supposition that 

 glacier ice underlies the moraines in places. 



We also observed another phenomenon, possibly due to collapsing of the moraine, 

 and consequent crackmg as the result of the removal by thawing of the underlying 

 ice. This phenomenon is what we called the " white paths," and is illustrated in 

 Fig. 2 of Plate LXXXV. At first we supposed that these paths, which evidently re- 

 presented depressions in the surface of the moraine, were formed by seals crawling 

 inland, but they were too closely set and widely distributed to be explained in such 

 a way. Possibly these " white paths " are contraction cracks, resulting from alternate 

 expansion and contraction of the moraines with change of season, or they may be 

 due to the creep of glacier ice beneath them. Neither of th^se suggested explana- 

 tions seems wholly satisfactory. 



In the direction of Cape Barne it was noticed that foreign erratics wei'e mostly 

 wanting. This is no doubt due to the fact that, as the last ice age reached its 

 climax and began to wane, the Cape Barne Glacier, then far larger than now, was 

 able to assert itself and overpowered the shrinking Ross Barrier, pushing it and its 



