How these furrows come into existence I have never been able clearly to comprehend, though I have often heard the phenomenon explained by men who imagined they understood it.

Whatever the cause and mode of formation may be, certain it is that little hills and valleys do get formed, and the sledge, as it crosses over them, bobs up and down like a boat in a chopping sea, with this important difference, that the boat falls into a yielding liquid, whereas the sledge falls upon a solid substance, unyielding and unelastic.

The shaking and jolting which result may readily be imagined.
There are other discomforts, too, in winter travelling.

So long as the air is perfectly still, the cold may be very intense without being disagreeable; but if a strong head wind is blowing, and the thermometer ever so many degrees below zero, driving in an open sledge is a very disagreeable operation, and noses may get frostbitten without their owners perceiving the fact in time to take preventive measures.

Then why not take covered sledges on such occasions?
For the simple reason that they are not to be had; and if they could be procured, it would be well to avoid using them, for they are apt to produce something very like seasickness.