. Elements of geology. Geology. 232 LYELL'S ELEMENTS OF GEOLOGY. Fossils of the Lias Origin of the Oolite and Lias. accumulated slowly in the sea of the lias, some being formed chiefly of one description of shell, such as ammonites, others of gryphites. Fossil plants.—Among the vegetable remains of the Lias, several species of Zamia have been Fig. 230. found at L^'^me Regis, and the re- mains of coniferous plants at Whitby. Fragments of wood are common, and often converted into argillaceous lime- stone. That some of this wood, though now petrified, was soft when it first lay at the bottom of t
. Elements of geology. Geology. 232 LYELL'S ELEMENTS OF GEOLOGY. Fossils of the Lias Origin of the Oolite and Lias. accumulated slowly in the sea of the lias, some being formed chiefly of one description of shell, such as ammonites, others of gryphites. Fossil plants.—Among the vegetable remains of the Lias, several species of Zamia have been Fig. 230. found at L^'^me Regis, and the re- mains of coniferous plants at Whitby. Fragments of wood are common, and often converted into argillaceous lime- stone. That some of this wood, though now petrified, was soft when it first lay at the bottom of the sea, is shown by a specimen now in the museum of the Geological Society, (see Fig. 230.) which has the form of an ammonite indented on its surface. Origin of the Oolite and Lias.—If we now endeavour to restore, in imagination, the ancient condition of the European area at the period of the Oolite and Lias, we must conceive a sea in which the growth of coral reefs and shelly limestones, after proceeding without interruption for ages, was liable to be stopped suddenly by the deposition of clayey sediment. Then, again, the argillaceous matter, devoid of corals, was deposited for ages, and attained a thickness of hundreds of feet, until ano- ther period arrived when the same space was again occupied by calcareous sand, or solid rocks of shell and coral, to be again succeeded by the recurrence of another period of argillaceous deposition. Mr. Conybeare has remarked of the entire group of Oolite and Lias, that it consists of repeated alternations of clay, sandstone, and limestone, following each other in the same order. Thus the clays of the lias are followed by the sands of the infe- rior oolite, and these again by shelly and coralline limestone, (Bath oolite, &c.;) so, in the middle oolite, the Oxford clay is followed by calcareous grit and " coral rag;" lastly, in the upper oolite the Kimmeridge clay is followed by the Weymouth sands and the Portland limestone
Size: 2219px × 1126px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlyellcharlessir17, bookcentury1800, booksubjectgeology
