CHAP. XXV.

OF THE TWENTY YEARS.

269

eighty million seven hundred and thirty-six thou-sand, being added, will make together one hundredand three million seven hundred and thirty-sixthousand pounds; but as the mines of Russia inthe early part of the period were less productivethan towards the end of it, we may make an allow-ance of the three millions seven hundred andthirty-six thousand pounds for that circumstance,and take the whole amount as one hundred mil-lions, or five millions annually.

that found in the lead in some of the northern mines. It issaid to have amounted to as much as one hundred and eightythousand pounds in value. On the whole term here considered,the amount here is hut small, and it affects the calculation ofHumboldt in too slight a degree to make any alteration neces-sary in the estimate he has formed.