There was no good building material convenient.

A stone house would cost a great deal of labour--as the stones would have to be carried nearly a mile, and in their hands too.

That would never do, as Von Bloom might only remain a short while at that place.

He might not find many elephants there, and of course would be under the necessity of going elsewhere.
Why not build a log-house?
you will say.

That would not be so much of a job, as part of the country was well wooded, and they had an axe.
True, part of the country was wooded, but in a particular manner.