到了1700年，弗吉尼亚州的边境已经向西远推到了瀑布线——上游河流倾泻于大西洋从而不能通航的点。
By 1700 the Virginia frontier had been pushed as far west as the fall line-the point upstream at which the rivers emptying into the Atlantic became unnavigable.
各主要滩段均不能满足万吨级船队的通航要求。
All the main rapid reaches cannot meet the navigation expectation of ten-thousand-tonnage fleet.
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