Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ch. xxvn.] aymestry limestone. 553 monly a micaceous stone, decomposing into soft mud, and contains^ besides the shells just quoted, a Lingula, which is common to it and the ' Tilestone ' (or Ledbury) beds at the base of the Old lied. The Orthis orbicularis, a round variety of 0. elegantula, is characteristic of the Upper Ludlow; and the lowest or mudstone beds contaiu ffliyn- chonella navicula (fig. 623), which is
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ch. xxvn.] aymestry limestone. 553 monly a micaceous stone, decomposing into soft mud, and contains^ besides the shells just quoted, a Lingula, which is common to it and the ' Tilestone ' (or Ledbury) beds at the base of the Old lied. The Orthis orbicularis, a round variety of 0. elegantula, is characteristic of the Upper Ludlow; and the lowest or mudstone beds contaiu ffliyn- chonella navicula (fig. 623), which is common to this bed and the Fig. 623. Ortlris Yar. orbicularis, Athyris (JRhynchonelld) navicula, J. Sow. Delbury. J. Sow. Upper Ludlow. Aymestry limestone; also in Upper and Lower Ludlow. Lower Ludlow. As usual in the strata of Primary periods older than the coal, the brachiopoclous mollusca greatly outnumber the lamilli- branchiate (see above, p. 543); but the latter are by no means unrep- resented. Among other genera, for example, we observe Avicula and Pterinea, Cardiola, Ctenodonta (subgenus of JVucula), Orthonota, and Modiola. Some of the Upper Ludlow sandstones are ripple-marked, thus affording evidence of gradual deposition; and the same may be said of the accompanying fine argillaceous shales which are of great thick- ness, and have been provincially named ' mudstones.' In some of these shales stems of crinoidea are found in an erect position, having evidently become fossil on the spots where they grew at the bottom of the sea. The facility with which these rocks, when exposed to the weather, are resolved into mud, proves that, notwithstanding their antiquity, they are nearly in the state in which they were first thrown down. Lower Ludloiv.—a. Aymestry Limestone.—The next group is a subcrystalline and argillaceous limestone, which is in some places 50 feet thick, and distinguished around Aymestry and at Sedgley by the abundance of Pentamerus LCn
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