Page:Popular Science Monthly Volume 90.djvu/611

 Popular Science Monthly

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��Telling the Age of Water-Marks On a Lake Shore

A RECENT investigation of the water level of lakes by two consulting en- gineers, one an American and the other a Canadian, resulted in the collection of interesting data on the age of water-marks and stains on the rocks along a lake shore. Moss and lichens, common vegetation in northern latitudes, play an important part in this study, the water stains on the rock being due to the absence or partial absence of one or more forms of these, lichens. The removal of these li- chens and the form- ation of a mark by standing water ma}- occur in a com- paratively short time, possibly in a season, but a num- ber of years are re- quired to change substantially the sharpness of a water line once formed.

One of the accom- panying illustrations showsclearly the ap- pearance of these stains or water- marks. It may be noticed that the marks are higher on the exposed face of the rock than around the corner where the rock is protected to some extent from wave action. The other illustration suggests the length alter a mark

����of time required to On this rock a high-water mark was cut in 1895 at the point indicated by the pencil. It is still plainly visible and practically unaltered, although it is no longer the high-water mark for that particular locality.

One of the most interesting series of water-marks left by large inland bodies of water may be seen on rocks which now He far above the level of Great Salt Lake. These rocks tell the story of the lake's 'gradual evaporation.

��Replacing Rags with Waste Tanbark in Making Coarse Paper

TO-DAY the price of plain everyday rags is soaring high above the clouds in company with thatof most commodities. Its use in the manufacture of paper has there- fore greatly diminished. Not that we are making less paper than before, but because a cheaper substitute has been found for the rags. This substitute is waste tanbark. In the manufacture of wall- paper alone fully eighty per cent of the rags previously used are being suc- cessfully replaced by it.

The greatest total saving that tanbark is effecting, how- ever, is in the pro- duction of felt shin- gles for roofing. The United States has been manufacturing nearly nine million square feet of these shingles each year. The material enter- ing into them weighs about two hundred and forty thousand tons. Of this, by far the greatest part has been made of rags. But now

over thirty per cent of this is being re- placed by the tan- bark, and the fin- ished product is as satisfactory as it ever was.

The tanbark is made up of the bark of oak and hemlock trees. Some seven hundred thousand tons of it had been going to waste each year. But now, after the valuable tannin has been extracted from the waste, every scrap of it is being put to this new usage. Even the worn-out tanbark flooring used in riding academies and for exhibition purposes may be used again in this way.

It would seem then that felt shingles for roofing would be one of the few manufac- tured articles the price of which has not been augmented by the war.

��On the rock shown in the illustration at the top a high-water mark was cut in 1895. In the oval appear water-marks and stains

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