In the lower Jura formations (the lias of Lyme Regis), the ink bag of the sepia has been so wonderfully preserved, that the material, which myriads p 272 of years ago might have served the animal to conceal itself from its enemies, still yields the color with which its image may be drawn.*
[footnote] *A discovery made by Miss Mary Anning, who was likewise the discoverer of the coprolites of fish. These coprolites, and the excrements of the Ichthyosauri, have been found in such abundance in England (as, for instance, near Lyme Regis), that, according to Buckland"s expression, they lie like potatoes scattered in the ground. See Buckland, "Geology considered with reference to Natural Theology", vol. i., p. 188-202 and 305.
With respect to the hope expressed by Hooke "to raise a chronology" from the mere study of broken and fossilized sh.e.l.ls "and to state the interval of time wherein such or such castrophes and mutations have happened," see his "Posthumous Works, Lecture", Feb. 29, 1688.
[Still more wonderful is the preservation of the substance of the animal of certain Cephalopodes in the Oxford clay. In some specimens recently obtained, and described by Professor Owen, not only the ink bag, but the muscular mantle, the head, and its crown of arms, are all preserved in connection with the belemnite sh.e.l.l, while one specimen exhibits the large eyes and the funnel of the animal, and the remains of two fins, in addition to the sh.e.l.l and the ink bag. See Ansted"s "Ancient World", p. 147.] -- Tr.
In other strata, again, nothing remains but the faint impression of a muscle sh.e.l.l; but even this, if it belong to a main dividion of mollusca,* may serve to show the traveler, in some distant land, the nature of the rock in which it is found, and the organic remains with which it is a.s.sociated.
[footnote] *Leop. von Buch, in the "Abhandlungen der Akad. der Wiss. zu Berlin in dem Jahr" 1837, s. 64.
Its discovery gives the history of the country in which it occurs.
The a.n.a.lytic study of primitive animal and vegetable life has taken a double direction: the one is purely morphological, and embraces, especially, the natural history and physiology of organisms, filling up the chasms in the series of still living species by the fossil structures of the primitive world. The second is more specially geognostic, considering fossil remains in their relations to the superposition and relative age of the sedimentary formations. The former has long predominated over the latter, and an imperfect and superficial comparison of fossil remains with existing species has led to errors, which may still be traced in the extraordinary names applied to certain natural bodies. It was sought to identify all fossil species with those still extant in the same manner as, in the sixteenth century, men were led by false a.n.a.logies to compare the animals of the New Continent with those of the Old. Peter Camper, Sommering, and Blumenbach had the merit of being the first, by the scientific application of a more accurate p 273 comparative anatomy, to throw light on the osteological branch of palaeontology -- the archaeology of organic life; but the actual geognostic views of the doctrine of fossil remains, the felicitous combination of the zoological character with the order of succession, and the relative ages of strata, are due to the labors of George Cuvier and Alexander Brongniart.
The ancient sedimentary formations and those of transition rocks exhibit, in the organic remains contained within them, a mixture of structures very variously situated on the scale of progressively-developed organisms. These strata contain but few plants, as, for instance, some species of Fuci, Lycopodiaceae which were probably arborescent, Equisetaceae, and tropical ferns; they present, however, a singular a.s.sociation of animal forms, consisting of Crustacea (trilobites with reticulated eyes, and Calymene), Brachiopoda ("Spirifer, Orthis"), elegant Sphaeronites, nearly allied to the Crinoidea,* Orthocerait.i.tes, of the family of the Cephalopoda, corals, and, blended with these low organisms, fishes of the most singular forms, imbedded in the upper silurian formations.
[footnote] *Leop. von Buch, "Gebirgsformationen von Russland", 1840, s.
24-50.
The family of the Cephalaspides, whose fragments of the species "Pterichtys"
were long held to be trilobites, belongs exclusively to the devonian period (the old red), manifesting, according to Aga.s.siz, as peculiar a type among fishes as do the Ichthyosauri and Plesiosauri among reptiles.*
[footnote] *Aga.s.siz, "Monographie des Poissons Fossiles du vieux Gres Rouge", p. vi. and 4.
The Goniat.i.tes, of the tribe of Ammonites,* a are manifested in the transition chalk, in the graywacke of the devonian periods, and even in the latest silurian formations.
[footnote] *Leop. von Buch, in the "Abhandl. der Berl. Akad.", 1838, s.
149-168; Beyrich, "Beitr. zur Kenntniss des Rheinischen Uebergangagebirges", 1837, s. 45.
The dependence of physiological gradation upon the age of the formations, which has not hitherto been shown with perfect certainty in the case of invertebrata,* is most regularly manifested in vertebrated animals.
[footnote] *Aga.s.siz, "Recherches sur les Poissons Fossiles", t. i., "Introd.", p. xviii.; Davy, "Consolation in Travel", dial. iii.
The most ancient of these, as we have already seen, are fishes; next in the order of succession of formation, pa.s.sing from the lower to the upper, come reptiles and mammalia. The first reptile (a Saurian, the Monitor of Cuvier), which excited the attention of Leibnitz,* is found in cuperiferous schist of the Zechstein of Thuringa; the Palaeosaurus and Thecodontosaurus of Bristol are, according to Murchison, of the same age.
[footnote] *A Protosaurus, according to Hermann von Meyer. The rib of a Saurian a.s.serted to have been found in the mountain limestone (carbonate of lime) of Northumberland (Herm. von Meyer, "Palaeologica", s. 299), is regarded by Lyell ("Geology", 1832, vol. i., p. 148) as very doubtful. The discoverer himself referred it to the alluvial strata which cover the mountain limestone.
The Saurians are found in large numbers in the muschelkalk,* in the keuper, and in the oolitic formations, where they are the most numerous.
[footnote] *F. von Alberti, "Monographie des Bunten Sandsteins, Muschelkalks und Keupers", 1834, s. 119 und 314.
At the period of these formations there existed Pleiosauri, having long, swan-like necks consisting of thirty vertebrae; Megalosauri, monsters resembling the crocodile, forty-five feet in length, and having feet whose bones were like those of terrestrial mammalia, eight species of large-eyed Ichthyosauri, the Geosaurus or "Lacerta gigantea", of Sommering, and finally, seven remarkable species of Pterodactyles,* of Saurians furnished with membranous wings.
[footnote] *See Hermann von Meyer"s ingenious considertions regarding the organization of the flying Saurians, in his "Palaeologica", s. 228-252. In the fossil specimen of the Pterodactylus cra.s.sirostris, which, as well as the loonger known P. longirostris (Ornithocephalus of Sommering), was found at Solenhofen, in the lithographic slate of the upper Jura formation, Professor Goldfuss has even discovered traces of the membranous wing, "with the impressions of curling tufts of hair, in some places a full inch in length."
In the chalk the number of the crocodilial Saurians diminishes, although this epoch is characterized by the so-called crocodile of Maestricht (the Mososaurus of Conybeare), and the colossal, probably graminivorous Iguandon.
Cuvier has found animals belonging to the existing families of the crocodile in the tertiary formation, and Scheuchzer"s "antediluvian man"
("h.o.m.o diluvii testis"), a large salamander allied to the Axolotl, which I brought with me from the large Mexican lakes, belongs to the most recent fresh-water formations of Oeningen.*
[footnote] *[Ansted"s "Ancient World", p. 56.] -- Tr.
The determination of the relative ages of organisms by the superposition of the strata has led to important results regarding the relations which have been discovered between extinct families and species (the latter being but few in number) and those which still exist. Ancient and modern observations concur in showing that the fossil floras and faunas differ more from the present vegetable and animal forms in proportion as they belong to lower, that is, more ancient sedimentary formations. The numerical relations first deduced by Cuvier p 275 from the great phenomena of the metamorphism of organic life,* have led, through the admirable labors of Deshayes and Lyell, to the most marked results, especially with reference to the different groups of the tertiary formations, which contain a considerable number of accurately investigated structures.
[footnote] *Cuvier, "Recherches sur les Oss.e.m.e.ns Fossiles", t. i., p.
52-57. See, also, the geological scale of epochs in Phillips"s "Geology", 1837, p. 166-185.
Aga.s.siz, who has examined 1700 species of fossil fishes, and who estimates the number of living species which have either been described or are preserved in museums at 8000, expressly says, in his masterly work, that, "with the exception of a few small fossil fishes peculiar to the argillaceous geodes of Greenland, he has not found any animal of this cla.s.s in all the transition, secondary or tertiary formations, which is specifically identical with any still extant fish." He subjoins the important observation "that in the lower tertiary formations, for instance, in the coa.r.s.e granular calcareous beds, and in the London clay,* one third of the fossil fishes belong to wholly extinct families.
[footnote] *[See "Wonders of Geology", vol. i., p. 230.] -- Tr.
Not a single species of a still extant family is to be found under the chalk, while the remarkable family of the "Sauroidi" (fishes with enameled scales), almost allied to reptiles, and which are found from the coal beds -- in which the larger species lie -- to the chalk, where they occur individually, bear the same relation to the two families (the Lepidosteus and Polypterus) which inhabit the American rivers and the Nile, as our present elephants and tapirs do to the Mastodon and Anaplotheriun of the primitive world."*
[footnote] *Aga.s.siz, "Poissons Fossiles", t. i., p. 30, and t. iii., p.
1-52; Buckland, "Geology", vol. i., p. 273-277.
The beds of chalk which contain two of these sauroid fishes and gigantic reptiles, and a whole extinct world of corals and muscles, have been proved by Ehrenberg"s beautiful discoveries to consist of microscopic Polythalamia, many of which still exist in our seas, and in the middle lat.i.tudes of the North Sea and Baltic. The first group of tertiary formations above the chalk, which has been designated as belonging to the "Eocene Period", does not, therefore, merit that designation, since "the "dawn of the world" in which we live extends much further back in the history of the past than we have hitherto supposed."*
[footnote] *Ehrenberg, "Ueber noch jetzt lebende Thierarten der Kreidelnldung", in the "Abhandl. der Berliner Akad.", 1839, s. 164.
As we have already seen, fishes, which are the most ancient of all vertebrata, are found in the silurian transition strata, p 276 and then uninterruptedly on through all formations to the strata of the tertiary period, while Saurians begin with the zechstone. In like manner, we find the first mammalia ("Thylacotherium Prevostii", and "T. Bucklandii", which are nearly allied according to Valenciennes,* with marsupial animals) in the oolitic formations (Stonesfield schist), and the first birds in the most ancient cretaceous strata.**