Now in every part of the world where the Stratified Rocks have been laid open to view, remains of this kind are found scattered on all sides in the most profuse abundance. In Europe, in America, in Australia, in the frozen wastes of Siberia, in the countless islands scattered over the waters of the Pacific, there is scarcely a single formation, from the lowest in the series to the highest, that, when it is fairly explored, does not yield up vast stores of shells, together with bones and teeth, nay, sometimes whole skeletons of animals; also fragments of wood, impressions of leaves, and other organic substances. [Illustration: Fig. 12.--Fossil Irish Deer (County Fermanagh). In the Museum of Trinity College, Dublin. From Haughton’s Manual of Geology] These Fossil Remains do not always occur in the same state of preservation. Sometimes we have the bone, or plant, or shell, in its natural condition; still retaining not only its own peculiar form and structure, but likewise the very same organic substance of which it was originally composed. Examples innumerable may be seen in the British Museum, or, indeed, in almost any Geological collection: the fine skeletons of ancient Irish Deer, which are exhibited in the Museum of Trinity College, Dublin, and of which all the bones are in excellent preservation, must be familiar to many of our readers. It happens, however, more frequently that the organic substance itself has disappeared, but has left an impression on the rock, that now bears witness to its former presence. Thus, for instance, when a shell has been dissolved and carried away by water percolating the rock, it has very often left after it, on the hard stone, a mould of its outer surface and a cast of its inner surface, with a cavity between corresponding to the thickness of the shell. In such cases we have the form, the size, and the superficial markings of the organic body, but we have no part of its original substance, and no traces of its internal structure. This form of fossilization, as Sir Charles Lyell has well put it, “may be easily understood if we examine the mud recently thrown out from a pond or canal in which there are shells. If the mud be argillaceous, it acquires consistency in drying, and on breaking open a portion of it, we find that each shell has left impressions of its external form. If we then remove the shell itself, we find within a solid nucleus of clay, having the form of the interior of the shell.”[70] In many cases the space first occupied by the shell is not left empty when the shell has been removed, but is filled up with some mineral substance, such as lime or flint. The mineral thus introduced becomes the exact counterpart of the organic body which has disappeared; and has been justly compared to a bronze statue, which exhibits the exterior form and lineaments, but not the internal organization nor the substance of the object it represents.