194 
ALASKA GLACIERS 
or spit was completed, another was built outside it, and so 
on to the number of six or more. The one next the sea 
has a crest considerably above high-tide, at the extreme 
limit reached by storm waves, and the top of it is covered 
by drift-wood, to which annual additions are doubtless 
made. The next bar, lying back of this and parallel to 
it, is six feet lower. It also is covered by drift-wood, but 
the wood is decayed, so that no sound logs were found. 
Two others are successively lower and have no drift¬ 
wood, and the innermost are so low as to be covered by 
the water of the bay. It is evident that each of these 
ridges of shingle was formed by storm waves at the shore, 
and we may assume that its crest height was originally as 
far above high-tide as the crest of the outer ridge is now. 
The existing differences in height have resulted from the 
gradual sinking of the land, and a rude indication of the 
rate of sinking is given by the drift-wood. The inner 
ridges were made so long ago that the drift-wood they 
originally bore has rotted away and disappeared. The 
age of the second ridge has given time for only the partial 
decay of the timber upon it, and the inference is that the 
island has sunk to the extent of six feet in a period less than 
that necessary for the complete destruction of logs through 
the processes of decay. 
