p. 266

278 Lake Michigan

It is estimated that the water which passes out of Lake Erie is the surplus or drainage, of an area of 335,515 square miles; and by recent measurements which appear to have been made with sufficient regard for accuracy it is ascertained that the quantity of water passing in the Niagara river at Black Rock is 22,440,000 cubic feet per minute* or about eighty and one eighths cubic miles per annum. This is equivalent to fifteen inches [of] perpendicular depth of water spread over the whole area of the country drained; and therefore something less than half the annual quantity of rain in this portion of the country. From these data it results that an increase of three inches in the quantity of rain in a year, [would] (other circumstances being the same), would cause an increase of 4,488,000 cubic feet per minute at Black Rock or an annual amount of 2,358,892 800,400 cubic feet, and requiring an increased depth of channel

* See Silliman's Journal for January 1844