[Frost and fire : natural engines, tool-marks and chips : with sketches taken at home and abroad by a traveller] . )id, but it gives a greatage for these Icelandic rocks, and for those on which they rest. At other spots streams have cut wide and deep channelsin lavas of the same kind. The river at G-odafoss, in the 91 north, has cut a deep channel, and has worked its way back-wards for some hundreds of yards. The smoothed water-wornsurface is plainly seen on cliffs far below the fall. The riveris large, so it must work faster than the Oxera ; but if one hascut 900 feet, while the other has onl
[Frost and fire : natural engines, tool-marks and chips : with sketches taken at home and abroad by a traveller] . )id, but it gives a greatage for these Icelandic rocks, and for those on which they rest. At other spots streams have cut wide and deep channelsin lavas of the same kind. The river at G-odafoss, in the 91 north, has cut a deep channel, and has worked its way back-wards for some hundreds of yards. The smoothed water-wornsurface is plainly seen on cliffs far below the fall. The riveris large, so it must work faster than the Oxera ; but if one hascut 900 feet, while the other has only cut two, they cannothave begim to work at the same time. Giving one river creditfor only one-third of the work done, the rate makes the age ofthe lava at Godafoss 150,000 years*. But where streams do not flow on the lava about Goda-foss, the wrinkles have not been worn off, so weathering hasnot deniided a quarter of an inch of igneous rock in that timeat least. Other Icelandic rivers have done a great deal of Brueni has drilled large pits, and it has scooped outsmooth channels of considerable depth. * 300 feet, at one foot in 500 years. 92 DENUDATION. At Merkiarfoss, near Hecla, a small stream has dug outa large trench, and it has drilled the most fantastic peep-holesthrough a black conglomerate of ashes and stones, and thisriver began to work after the volcanic momitain had grown. At Skogarfoss, a river falls over a cliff on a sea-beach,and it has dug backwards into the hill for some fifty or sixtyyards. It began to dig after the sea had done its undermin-ing, and had retired towards the horizon away from the baseof the old sea-cliff. At the wearing rate the sea made the cliff75,000 years ago.* All these times may be wrongly calculated; they may beto
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