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The grounds on which they base that supposition are these: That if you go through the enormous thickness of the earth's crust and get down to the older rocks, the higher vertebrate animals the quadrupeds, birds, and fishes cease to be found; beneath them you find only the invertebrate animals; and in the deepest and lowest rocks those remains become scantier and scantier, not in any very gradual progression, however, until, at length, in what are supposed to be the oldest rocks, the animal remains which are found are almost always confined to four forms 'Oldhamia', whose precise nature is not known, whether plant or animal; 'Lingula', a kind of mollusc; 'Trilobites', a crustacean animal, having the same essential plan of construction, though differing in many details from a lobster or crab; and Hymenocaris, which is also a crustacean.

"Lingula flags" of Dolgelly, and Ffestiniog; N. Wales. Hymenocaris vermicauda, Salter. A phyllopod crustacean. Lingulella Davisii, M'Coy. a. One-half natural size. b. Olenus micrurus, Salter. Next below the Tremadoc slates in North Wales lie micaceous flagstones and slates, in which, in 1846, Mr.

The grounds on which they base that supposition are these: That if you go through the enormous thickness of the earth's crust and get down to the older rocks, the higher vertebrate animals the quadrupeds, birds, and fishes cease to be found; beneath them you find only the invertebrate animals; and in the deepest and lowest rocks those remains become scantier and scantier, not in any very gradual progression, however, until, at length, in what are supposed to be the oldest rocks, the animal remains which are found are almost always confined to four forms 'Oldhamia', whose precise nature is not known, whether plant or animal; 'Lingula', a kind of mollusc; 'Trilobites', a crustacean animal, having the same essential plan of construction, though differing in many details from a lobster or crab; and Hymenocaris, which is also a crustacean.

The grounds on which they base that supposition are these: That if you go through the enormous thickness of the earth's crust and get down to the older rocks, the higher vertebrate animals the quadrupeds, birds, and fishes cease to be found; beneath them you find only the invertebrate animals; and in the deepest and lowest rocks those remains become scantier and scantier, not in any very gradual progression, however, until, at length, in what are supposed to be the oldest rocks, the animal remains which are found are almost always confined to four forms Oldhamia, whose precise nature is not known, whether plant or animal; Lingula, a kind of mollusc; Trilobites, a crustacean animal, having the same essential plan of construction, though differing in many details from a lobster or crab; and Hymenocaris, which is also a crustacean.