On masses of ice

From The Adventures of Captain Hatteras by Jules Verne:

'They scarcely leave a passage for the [brig] Forward. Just examine that immense plain over there.'

'The whalers call that in our language an icefield, that is to say a continued surface of ice the limits of which cannot be perceived.'

'And on that side, that broken field, those long pieces of ice more or less joined at their edges?'

'That is a pack; if it was of a circular form we should call it a patch; and, if the form was longer, a stream.'

'And there, those floating icebergs?'

'Those are drift ice; if they were a little higher they would be icebergs or hills; their contact with vessels is dangerous, and must be carefully avoided. Here look over there: on that iceberg there is a protuberance produced by the pressure of the icebergs; we call that hummock; if that protuberance was submerged to its base we should call it a calf. It was very necessary to give names to all those forms in order to recognise them.'

'It is truly a marvellous spectacle!' exclaimed the doctor, contemplating the wonders of the Boreal Seas; 'There is a field for the imagination in such pictures!'