Star-fish, the asteria of Linnaeus, are found in a fossil state, but they are by no means abundant ; a circumstance easily accounted for when their soft and perishable nature is considered. If the specimens found in a fossil state are not actually the same as existing ones, the resem blances are very close. They occur principally in the chalk, and their impressions are also found in flints. Four teen or fifteen species have been described, and the ana logies of most of them to living species have also been noted.
Echini are a very common class of fossils, occurring through nearly all the strata, even from the primary ar gillaceous schist to the chalk, and possessing distinct mi neral characters accordingly. They are also found filled with flint, thus forming moulds. Their species are also frequently found detached from the body, and imbedded by themselves in the stones, and the bodies that are found are also, as might easily be foreseen, frequently naked, having lost their spines before they were petrified. The fossil species are very numerous. The first division of this extensive genus, the anocysti of Linck, are found both in the fossil and living state; but the catocysti, divid ed into many species, are as yet only known as fossils. In the other divisions, some are found living, and not fossil, and the reverse ; but as, without numerous figures, these species could not be rendered intelligible, We shall close our sketch of these tribes altogether.
Of Coral Formations, and of the extent of the areous produce of Marine Animals.
There is a circumstance, however, respecting the fossil existence of the animals of this tribe, which cannot be passed over, since it is of far higher interest than any thing which appertains to the history of organic remains, inter esting as that subject is in all its bearings. This part of the subject is, however, connected also with the history of the living species. If that connection is here peculiarly important, it must, however, be remembered, that, with respect to all the organic fossils, their chief interest is derived from the relations which they bear to the existing kinds, and from the effects which they have on the struc ture of the earth. We are surprised at the immense accumulation of shells which form the secondary calcare ous strata, or which, if they do not actually produce these, contribute most materially to their bulk, as well as to their chemical nature. And, in examining them, we cannot help being struck with the immense additions which the solid crust of the earth has received from the labours of animals, which, employed only in forming their own habitations, have, in the progress of time, generated mountains ; as we may safely say, when we examine the enormous strata into which they enter as principal and constituent parts.
Still, however, these do not make that impression on us which they ought ; because, seeing these rocks as we do, mixed with others, long deserted by the sea and by their former inhabitants, and now divested of all marks of life, and, except to the eye of a geologist, of all marks of their former origin, we are apt to pass them by, and think that the surface of the earth might have been much the same had these animals never existed, or had they remained at the bottom of that ocean where they lived and died. But when we trace this very act in its progress, when we can follow with our eyes the increments which the land is ac tually undergoing in consequence of the labours of subma rine animals, we receive a very different impression re specting their importance ; and, in watching the hourly formation and increase of the coral islands, begin to be more sensible of the vast importance of this race of be ings, and of the immense changes which all the marine tribes must have produced on the chemical nature, as well as on the structure and disposition, of the superficial or more recent strata.
With respect, now, to the operations of shell fish, pro perly speaking, we know that they are at this moment forming immense strata under the waters, just as they must have done in times long past, and before they could have produced the rocks which we now behold above the ocean. Whether these are ever destined to rise above the sea, or when that may happen, we cannot conjecture ; al though, were we to reason from analogy derived from past events, we should conclude it was probable, unable as we are to assign the mode in which such an event is to be brought about. Should it happen, new calcareous strata will be found on the surface of some future earth, and the fossil remains of those days will be the living species of our own. As the retrospective part of this question forms one of the most interesting of all the deductions that are to be drawn from the study of fossil shells, and is peculi arly a branch of those geological questions that depend on this study, we shall offer our readers a few remarks on it in this place, that we may not again disturb the descrip tions of the few fossil shells to which we have been oblig ed to limit this examination.