The Wealth of Nations by Part 2 Chapter 3 Page 29

The same quantity of money would in this case equally have remained in the country, and there would besides have been a reproduction of an equal value of consumable goods. There would have been two values instead of one.

The same quantity of money, besides, cannot long remain in any country in which the value of the annual produce diminishes. The sole use of money is to circulate consumable goods. By means of it, provisions, materials, and finished work, are bought and sold, and distributed to their proper consumers. The quantity of money, therefore, which can be annually employed in any country must be determined by the value of the consumable goods annually circulated within it. These must consist either in the immediate produce of the land and labour of the country itself, or in something which had been, purchased with some part of that produce.