132 The Ahierlcan Geohxjht. February, 1897 
produce marked changes upon the surface. To me the evi- 
dence of the amount and rapidity of weathering and erosion 
in the Arctic came as such a surprise that I wish to call espe- 
cial attention to it. 
One might expect that nearly the entire action of weather- 
ing in the higher latitudes would be that of mechanical de- 
struction, but such is not the case. Possibly because crevices 
are opened by the frost, the rocks readily and rapidly decay 
as a result of the chemical changes of the minerals. This 
disintegration of the rock has been slight wherever it has 
been protected by even a thin soil or vegetable covering. It 
is upon the exposed rock face, nearly bare of vegetation, and 
open to all the changes of weather that the rapid disintegra- 
tion is noticed. Hence these chemical changes are not sensibly 
dependent upon the presence of vegetable acids. It is true 
that on nearly all exposed rocks there are many lichens, but 
these are hardly competent to furnish much vegetable material 
to the percolating water. The oxygen and carbon dioxide of 
the air, working with the water, are the chief elements of 
change. As a result of these chemical changes the rock is 
often discolored by iron salts, and considerably altered near 
the surface; but nowhere has it been in operation long enough 
to have caused distinct soil of decayed rock particles. 
While notwithstanding the general absence of vegetation, 
and the low temperatures of the water, chemical disintegra- 
tion is actually in progress, and apparently not slowly opera- 
ting, the chief weathering that is seen is that of mechanical 
kind. One very important agent of this change is tlie lichen. 
Few parts of the world will yield a more abundant lichen flora 
than this northern country, north of the timber belt. The 
ledges, boulders and even the tiny pebbles, are almost every- 
where lichen-covered, and as they grow these must be per- 
forming a mechanical work of rock disintegration of high im- 
portance. 
It is of course in the decided changes of temperature, and 
the extremes of cold in winter, that we are to find the most 
energetic agents of weathering in these high latitudes. The 
expansion and contraction of minerals with the ch^inges of the 
temperature, and the effect of frost in the crevices, are active 
agents in breaking up the rocks. With the extremes of cold 
