… is from Book IV, Chapter 3  – on pages 497-498, Vol. 1, of the 1981 Liberty Fund edition  – of Adam Smith’s 1776 An Inquiry Into the Nature and Causes of the Wealth of Nations :
The balance of produce and consumption may be constantly in favour of a nation, though what is called the balance of trade be generally against it. A nation may import to a greater value than it exports for half a century, perhaps, together; the gold and silver which comes into it during an this time may be all immediately sent out of it; its circulating coin may gradually decay, different sorts of paper money being substituted in its place, and even the debts, too, which it contracts in the principal nations with whom it deals, may be gradually increasing; and yet its real wealth, the exchangeable value of the annual produce of its lands and labour, may, during the same period, have been increasing in a much greater proportion. The state of our North American colonies, and of the trade which they carried on with Great Britain, before the commencement of the present disturbances, may serve as a proof that this is by no means an impossible supposition.