. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 32 FRESHWATER AND MARINE FORMATIONS. [Cii. in. stems, as well as the seed-vessels, of these plants occur both in modern shell marl and in ancient freshwater formations. They are generally Fig. 53. Fig. 64. Chara medicaginula ; fossil. Upper Eocene, Isle of Wight. a. Seed-vessel, magnified 20 diameters. &. Stem, magnified. Chara elasUca ; recent. Italy. a. Sessile seed-vessel between the divisions of the leaves of the female plant. b. Magnified transverse section
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 32 FRESHWATER AND MARINE FORMATIONS. [Cii. in. stems, as well as the seed-vessels, of these plants occur both in modern shell marl and in ancient freshwater formations. They are generally Fig. 53. Fig. 64. Chara medicaginula ; fossil. Upper Eocene, Isle of Wight. a. Seed-vessel, magnified 20 diameters. &. Stem, magnified. Chara elasUca ; recent. Italy. a. Sessile seed-vessel between the divisions of the leaves of the female plant. b. Magnified transverse section of a branch, with five seed-vessels, seen from below upwards. composed of a large tube surrounded by smaller tubes ; the whole stem being divided at certain intervals by transverse partitions or joints. (See b, fig. 53.) It is not uncommon to meet with layers of vegetable matter, impres- sions of leaves, and branches of trees, in strata containing freshwater shells ; and we also find occasionally the teeth and bones of land quad- rupeds, of species now unknown. The manner in which such remains are occasionally carried by rivers into lakes, especially during floods, has been fully treated of in the " Principles of ;* The remains of fish are occasionally useful in determining the fresh- water origin of strata. Certain genera, such as carp, perch, pike, and loach (Cyprinus, Perca, £Jsox, and Cobitis), as also Lebias, being pe- culiar to freshwater. Other genera contain some freshwater and some marine species, as Cottus, Mugil, and Anffuilla, or eel. The rest are either common to rivers and the sea, as the salmon ; or are exclusively characteristic of salt water. The above observations respecting fossil fishes are applicable only to the more modern or tertiary deposits ; for in the more ancient rocks the forms depart so widely from those of ex- isting fishes, that it is very difficult, at least in the present state of sci- ence, to derive any positive information
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
