The Quarterly journal of the Geological Society of London . larger animal, arenumerous similar series of much smaller size, and also many singleindents not placed in the regular transverse curves before noticed. That these are not the tracks of marine worms is at once evidentfrom their arrangement in regular series, and from their each taperingbackwards, as well as lying parallel to each other. The section ofeach indent is subtriangular, so that it was probably made by somesharp instrument; and their shape tapering backwards and positionin parallel series indicate a rapid movement, such as wou
The Quarterly journal of the Geological Society of London . larger animal, arenumerous similar series of much smaller size, and also many singleindents not placed in the regular transverse curves before noticed. That these are not the tracks of marine worms is at once evidentfrom their arrangement in regular series, and from their each taperingbackwards, as well as lying parallel to each other. The section ofeach indent is subtriangular, so that it was probably made by somesharp instrument; and their shape tapering backwards and positionin parallel series indicate a rapid movement, such as would be given 210 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 14, by the spinous feet or abdomen of some crustaceous animal. As thereis every reason to believe that Trilobites had soft feet, they could nothave made such indentations with these instruments, and as theonly species known in these beds—the Olenus micrurus—had anobtuse rounded tail, it could not have made the marks with must look then to the possibility of their having been made by. the Hymenocaris, a shrimp-like animal, whose abdomen does possessthe requisite sharp prongs at its extremity, having in particular onelarge spine which seems to be exactly the instrument fitted for thepurpose. It is well known, that, when in rapid or violent movement,the Crustacea can strike vigorously with the abdomen, and so gain the 1853.] CUMMING GLACIAL DEPOSITS, ISLE OF MAN. 211 impetus necessary for advancing or retreating. And there is so mucliresemblance between these indented tracks, and those produced by thecommon Shrimp at ebb-tides, that the observer cannot help suspect-ing them to have been produced by this*,—perhaps, the oldest ofcrustaceans, in its movements along the bottom, or (what is moreprobable) over the sand at the extreme edge of the waves. The smaller marks were of course made by younger individuals ofthe species, whatever that may have been. But why should the in-dentations be parallel and arranged
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
