117 



ORGANIC REMAINS. 



ORGANIC REMAINS. 



118 



which cover coal; for the large cylindrical sterna of Stgillaria and 

 Lepidodendron lie flat as paper between the laminae of shale, but 

 appear with a depressed elliptical section when they lie obliquely 

 across the grits, and retain their cylindrical figure whenever they 

 stand erect in the rocks. 



The conditions under which the remains of animals are presented 

 vary very much. The conditions of preservation hi which fossil plants 

 appear may be thus classed : 



1. The plant little altered; as in the brown coal-formations of the 

 Rhine, and in a particular case at Gristhorp near Scarborough, among 

 the Oolites, where Solmitet Murrayana of Lindley is found flexile, 

 elastic, and with its tissues distinct. The same thing was observed by 

 the author at Ardwick near Manchester, in the coal formation. 



2. The plant carbonised to jet or coal. This conversion of the 

 vegetable substance is very common in clays of every geological age ; 

 plentifully so in the coal formation. 



3. The substance of the plant entirely removed from the place that 

 it occupied, leaving a hollow where it was deposited. This happens in 

 coarse gritstone, as near Leeds. 



4. The cells of the plant filled with extraneous matter, as carbonate 

 of lime in Lepidodendron Harcourtii (see the ' Fossil Flora of Great 

 Britain'), pyrites in the fruits of Sheppey, silica hi the wood of 

 Woburn. 



The remains of the animal kingdom present a parallel series : 



1. Bones of Vcrtebrata generally, scales of fishes, the coverings of 

 Cruttacea, are often but slightly changed from their original composi- 

 tion. They often retain the gelatinous parts of their mass. 



2. Shells, corals, aid Echinodermata, composed of carbonate of lime 

 with gelatin, have in some cases (and very often among tertiary strata) 

 not lost the whole of their gelatinous part. From this condition of 

 little change there is every gradation observable, till (in the oolites 

 particularly) the whole of the organic substance has been entirely 

 removed, and a cavity is left in its place. The sides of this cavity 

 retain the impression of the external surface of the coral or shell ; 

 and it not unfrequently happens that in the cavity once occupied by a 

 shell is an almost unattached mass of stone, which filled the interior 

 of the shell, and represents the figure of the animal, in several respects, 

 perfectly. 



3. Into this cavity carbonate of lime has been again introduced in 

 solution, so as to become clearly crystallised in solitary rhomboids, or 

 in a connected mass, replacing completely the gelatin and carbonate of 

 lime which composed the original shell; in other cases silica, and, 

 rarely, iron pyrites, fill up the vacuity. 



4. The greensand formations show abundance of examples of the 

 impregnation of the calcareous substance of shells, corals, and Echino- 

 dermata, with a siliceous infiltration. 



The occurrence of organic remains is not known to be dependent 

 on depth below the surface of the earth or on particular height 

 above it. Fossil plants occur in our deepest collieries, and fossil shells 

 crown very lofty points of the Alps and Pyrenees. Yet, because of 

 the limited thickness of the strata, and the entire absence of organic 

 reliquiae from the granite masses below them, it is evident that at the 

 depth of a few thousand yards below the surface, in most situations, 

 the traces of ancient life end. In like manner, because in general the 

 lower strata, in which few or no organic forms remain, rise to the 

 highest ground, many mountain ranges are almost or absolutely 

 deficient in fossils. Upon the whole these are most numerous in the 

 lower parts of the earth s surface, because the formations there occurring 

 are gomrally of a later origin than the stratified rocks which are 

 uplifted into mountain chains. 



In modern oceans the occurrence of marine Mollutca, Zoophyta, &c., 

 in a living state, is either known or inferred to be limited to moderate 

 depths, from 10 to 100 or 1000 feet; when therefore we reflect on the 

 vast abundance of shells hi the Silurian strata, buried beneath several 

 thousand feet of old red-sandstone, or of the comparable phenomena 

 presented by the mountain limestone shells which are covered by 3000 

 or 5000 feet of coal strata, we see clearly in these cases the probability 

 (independent of the proof deduced from considering the nature and 

 position of the rocks) of the occurrence of great upward and downward 

 movements affecting large breadths of the ancient oceans. 



Shells, fishes, and Polypifera affect, while living, peculiar situations ; 

 the rocky, sandy, and argillaceous parts of the sea-bed yield Jladiata 

 and Mollutca in very unequal abundance ; and it is worth inquiry how 

 far such relations and peculiarities can be discovered among fossil 

 reliquiae. If anciently vegetables were swept down by inundations 

 from the land and buried in marine or fresh-water deposits, we ought 

 to find some correspondence between these deposits and the sediments 

 which now, in various parts of the world, are drifted with the trees 

 and herbs to great inland lakes, [estuaries, or the open sea. This 

 expectation in justified by observation. It is almost exclusively in 

 arenaceous and argillaceous strata, which for other reasons geologists 

 have infeired to be detrital deposit*, that we find the specimens of 

 terrestrial herbs and trees, mostly fragmentary, and often accumulated 

 in irregular patches. This is well seen in the arenaceous strata of the 

 Yorkshire coast. Again, it is principally in limestones that we find 

 the lamelliferous corals and a large proportion of the Echinodermata, 

 and this is in accordance with observation of the analogous living races. 



But the circumstance to which the laws of distribution of organic 



remains in the earth are most distinctly and constantly related, is the 

 antiquity of the strata. This will appear from the following brief 

 statements. 



In the oldest of all the strata known to geologists, the gneiss and 

 mica-schist systems, which repose upon the unstratified granites and 

 congeneric rocks, few or rather no traces of organic life appear. Hence 

 it is that fossila appear excluded from particular geographical areaa, 

 as for example frequently from the interior parts of great mountain 

 ranges, which are generally composed in a considerable proportion of 

 these ancient primary strata. 



On the contrary, among the more recent of the marine strata for 

 example, the eocene tertiary strata of London and Paris, the number 

 of organic fossils is prodigiously great. If these contrasted cases were 

 the only ones which appeared to suggest a law that ' the number of 

 organic fossils in the strata continually augmented from the earliest 



Erimary to the latest tertiary rocks,' they would deserve attention ; 

 ut the supposition becomes changed into exact inference by comparing 

 successively the systems of strata on a uniform plan. [GEOLOGY.] 



Such being the facts with regard to the number of species of organic 

 remains in the several systems of strata, we may next inquire as to 

 the distribution of the several kinds of fossil plants and animals. 

 Taking the broadest view of the subject, we may represent the distri- 

 bution of the classes of plants and animals in compendious tables. 



Distribution of the Clattei of Plants. 



The reader will not fail to remark that the classes belonging to the 

 columns marked below, are represented in all the fosailiferous strata, 

 and that they all contain hard conservable parts, more abundantly 

 than any other of the classes. They are alao principally marine, some 

 of them exclusively so. These facts should make us scrupulous in 

 believing that the full system of ancient organic life is disclosed to us 

 by the series of organic fossils preserved in the earth. 



Distribution of the Clones of Invertebral Animals. 



t t t 1 1 J 



Fishes are the only class of Vertebrala found in all the systems of 

 strata. Reptiles begin to appear (if not in the Carboniferous system) 

 certainly in the next above. Birds and Mammalia appear locally and 

 rarely in the Oolitic rocks. If, lastly, we enquire in what part of the 

 series of aqueous deposits the remains of Man have been found, the 

 answer furnished by modern observation is very different from the 

 fanciful conjectures common in the 17th century. Then the remains 

 of men, " evidences of the deluge " (as Scheuchzer calls his imaginary 

 fossil man, but real fossil salamander !) [AMPHIBIA], were supposed to 

 be common in rocks of every age ; now we are not able to quote a 

 single authentic example of any such occurrence except in loose surface 



