Quote from The Far Side of the World, Chapter Eight -
He had gone on to think about ways of making fire when Stephen said, 'And these things being so, I became convinced that the large rounded object about the size of a moderate turtle but more lumpish there on the strand to your right, where the water is lapping it, could not be a boulder. No, I have more than half persuaded myself that it is an enormous piece of ambergris, washed up by the sea.'
'Have you not been to look at it?'
'I have not. The association of rarity, wealth and so on instantly brought that unfortunate brass box to my mind, the most unwelcome box from the Danaë packet which is now aboard the Surprise; and as recollection came to me, so I grew perfectly convinced, as by a revelation, that rats or cockroaches or book-worms or various moulds were eating its contents, to our utter ruin - eating them with tropical avidity, a million of money. The thought fairly cut my legs from under me, and I have sat here ever since.'
'It is a thousand to one we shall never have any need of the brass box, nor of the ambergris unless it can be eaten,' said Jack to himself. 'And if th weather goes on breaking up like this - if it really comes on to blow and Surprise is driven a great way to leeward, then it is ten thousand to one or more, much more.' But aloud, giving Stephen a hand up, he said, 'Let us go and have a look. If it is ambergris, we are made men: we have but to go to the nearest dealer and change it for its weight in gold, ha,ha, ha!'
It was not ambergris: it was a piece of crystalline limestone, mottled and in part translucent, and it fairly stupefied Maturin. 'How can such things be?' he asked, gazing out into the offing. 'There is no question of glaciers, icebergs ... How can such things possibly come about? There is the boat. I have it,' he cried. 'This rock was brought tangled in the roots of a tree, a great tree swept away by some remote flood or tornado, cast up the Dear knows how many thousands miles drifting, and here decaying, leaving its incorruptible burden. Come, Jack, help me turn it - see,' he cried with a shining face as it heaved over, 'in these fractuosities there are still traces of my roots. What a discovery!'
'What did you mean when you said boat?'
'Why, our boat, of course. The big one, the launch, come to fetch us, as you always said it would. Lord, Jack,' he said, looking up with an entirely different expression, 'how in God's name shall I ever face them at all?'
A perfect representation of the way both of these men's minds work in completely different ways and yet work so well together.
Stephen measures things in 'turtle sizes' and falls easily into the depths of despair by the sight of an object setting off reflections that cause him to sink into a slough of despondency, unable to move but then his emotions are rapidly reversed into a high state of excitement and joy when he believes he has hit on the perfect explanation for the presence of a geological oddity. So excited that the arrival of the rescue boat seems to be barely worth a mention. Then sinks back into a funk almost immediately when he realises how difficult and embarrassing it will be to face his saviours in the rescue boat. No wonder he needs laudanum to dampen down the volatility of his emotions.
While in comparison Jack is supremely practical in his way of thinking and at the same time so solicitous of his friend's state of mind he humours him by encouraging him to check out the lumpish rock to see whether they have become made men. He completely ignores Stephen's theories concerning the provenance of the 'lump of limestone' and focuses entirely on Stephen's throwaway line about the 'boat'. Jack the calm and practical one, trying to protect and support his friend as always.