The unenclosed grounds, about Louisville and Shippingsport, are extensive, and afford pasturage to great numbers of domestic animals. They are, however, much overrun with luxuriant weeds. The datura strammonium, which is common in every part of Ohio, is sometimes eaten by sheep; and the spiny capsules of the seed, when about half ripened, we have seen eaten with apparent avidity by cows. In addition to this loathsome plant, the common May-weed (anthemis cotula) has become abundant {27} in all the waste-grounds, to the exclusion of the native plants. A few of these, which keep their places with the greatest obstinacy by the road sides, are the sida abutilon and S. spinosa, and the verbena hastata; while the thistles, chrysanthemums and Johnsworts, so common about old fields in New England, are not to be met with. The eleusine mucronata, of _Pursh_, is one of the most frequent grasses along the streets. The Silver Creek hills are elevated about one hundred and fifty or two hundred feet above the level of the country in the rear of Jeffersonville.[039] They form a continuous range, crossing the country from north to south. On the Kentucky side they constitute the commencement of a rugged and barren district, called the _Knobs_, and extending far to the south.[040] At some remote period this range may have formed a barrier, extending across what is now the immediate valley of the Ohio, and retarding the retreat of the waters from the tract above the falls.[041] Coal occurs frequently in this range of hills, on the north side of the Ohio; quarries have been opened near the Blue river, in Indiana, about the two Pidgeons, opposite the mouth of Green river, and in various other places.[042] The larger steam-boats which run on the Mississippi, and the Ohio, ascend usually no farther than Shippingsport; and several of them remain at this place, during several months of the summer, while the water is too low to admit their passing up and down the rivers. This time it is often necessary to spend in repairs of various kinds. The high steam-engines require frequent repairs, and in the difficult navigation of the Mississippi the hulks of vessels are often injured. It frequently happens that the boats built at Pittsburgh, and other places near the sources of the Ohio, are, within three or four years after they {28} are launched, in a condition to require the planking of the hulk to be replaced with new timber. These boats are usually planked with the upland white oak: we have been informed that such as are built lower down on the river, and of timber found in the low grounds, are more durable. FOOTNOTES: