to this the earth at the same time was cleft with great cracks or
fissures, which reached down through many miles of the planet's crust
to the central fires and released the boiling rocks imprisoned in its
bosom, and these poured to the surface, as igneous, intrusive, or
trap-rocks. Where the great breaks were not deep enough to reach the
central fires, they left mighty fissures in the surface, which, in
the Scandinavian regions, are known as _fiords_, and which constitute
a striking feature of the scenery of these northern lands; they are
great canals--hewn, as it were, in the rock--with high walls
penetrating from the sea far into the interior of the land. They are
found in Great Britain, Maine, Nova Scotia, Labrador, Greenland, and
on the Western coast of North America.

David Dale Owen tells us that the outburst of trap-rock at the Dalles
of the St. Croix came up _through open fissures_, breaking the
continuity of strata, without tilting them into inclined planes."[1]
It would appear as if the earth, in the first place, cracked into
deep clefts, and the igneous matter within took advantage of these
breaks to rise to the surface. It caught masses of the sandstone in
its midst and hardened around them.

These great clefts seem to be, as Owen says, "lines

[1. "Geological Survey of Wisconsin, Iowa, and Minnesota," p. 142.]

{p. 52}

radiating southwestwardly from Lake Superior, as if that was the seat
of the disturbance which caused them."[1]