More than that, the temperature may rise as we go down into the earth and afterwards fall again.

There may be a stratum of close-grained rock, possibly containing metal, coming up from the interior in an oblique direction and bringing the heat towards the surface; then below that there may be vast regions of other rocks which do not readily conduct heat, and which do not originate in heated portions of the earth's interior.

When we reach these, we must find the temperature lower, as a matter of course.

Now I have really done this.
A little over five miles down my thermometer registered ninety-one, and after that it began to fall a little.

But the rocks under us are poor conductors of heat; and, moreover, it is highly probable that they have no near communication with the source of internal heat." "I thought these things were more exact and regular," said she; "I supposed if you went down a mile in one place, you would find it as hot as you would in another." "Oh no," said he.