There is thus no difficulty in accounting for the presence of the insects, which are such as would naturally alight on trees, and, being entangled in those exudations, become embalmed in the gum. This opinion is fully confirmed by the corresponding fact of flies and ants found at present in the resins of many trees. In some of the resins brought from the West Indies, one of which is known by the name of gum animi, this occurrence is very common. These specimens are even sold for amber, which they very much resemble; and, in examining the nature of the fossil insects, it is necessary to attend to this distinction ; as, from igno rance of it, some naturalists have even pronounced on the species of insect inclosed, as they had imagined, in amber. It is not difficult to distinguish between the two, and it is most easily done by touching the surface with a hot iron ; as the smell of amber and that of the resins are perfectly distinct, and well known to every one. This test is so easy and convenient that we need not name any others.
Excluding now these false specimens, it will be found that the occurrence of insects in amber is rare. It is also impossible to ascertain the species, whatever may be ima gined ; and, indeed, it is probable that, like the vegetable remains of the same date, we are not to look for them among existing ones. It is not even known how many kinds there are ; but, on general principles, we might con clude that they should be numerous, as so many insects must have had the opportunity of thus entangling them selves. Insects, both with wings and without, have been found; the former having a general resemblance to the bees, and the dipterous flies, and the latter to ants.
The next, and only other case of insects in a fossil state, is so rare, that only two examples have yet occurred ; and one of these has been described by Dr. Macculloch, in his account of vegetables imbedded in chalcedony, in the Transactions of the Geological Society. This specimen, (as it is worth while to trace its history,) was purchased by our well known countryman, Mr. Byers, at Rome, and is now in the possession of the Countess of Powis. The animal is the pupa of a lepidopterous insect, and is quite perfect ; being involved, like the vegetables which we de scribed formerly, in a chalcedony. We may add, that a si milar specimen was lately in the possession of a dealer in London. The manner in which this petrifaction may have been produced, may be understood from our former re marks on the minute vegetables that have been preserved in the same manner.
We must yet, however, mention some terrestrial which rest on the authority of Llwyd, and for which we have only his figures, one or two of which are not very intelligible. These, he says, he found in shale, in the coal series ; a situation which, as we have already seen, is one in which such terrestrial animals might easily have been preserved. Two of the figures which he has given resemble the genus Cimex, and might easily have been aquatic species of this tribe ; since, if of sufficient hard ness, as many of them are, there is no difficulty in conceiv ing how they should have been entangled and preserved in the mud of the lakes, which was the undoubted origin of these shales. We ought rather to be surprised that
they are not more frequent. Of the other two, one has wings, and though he calls it a Searabxus, it is also more likely to have belonged to one of the aquatic insects; to Dytiscus, perhaps, or some analogous genus of similar construction. His last figure appears to have been drawn from some specimen so mutilated and distorted, that it is impossible to pronounce any opinion on its analogies ; though it is probably also an aquatic animal.
Of Fossil Zoophytes.
The first of these which we shall mention is the tubipora, or, according to the fashion adopted by mineralogists in naming the fossil animals, tubiporite. A species resem bling in a great degree the Tubipora musica, is found in the Derbyshire limestone, and in Wales, and some of them, still retaining traces of the red colour, indicate still more nearly their affinity to that living species. When imbed ded in marble, it sometimes communicates a reddish tinge to the stone. These fossils sometimes contain much sili ceous matter, as well as calcareous, so as even to be capable of scratching glass. Other species of this genus, equally irreconcilable to any living species, though resembling some, occur in different places in beds of limestone, as in the Mendip hills in Westmoreland, &c. We shall not at present specify the strata in which these and other fossils are found, because it will be more useful to give a synoptic view of the whole hereafter.
As we dare not, within our limits, attempt even to enu merate all the species of any genus that have been named, we shall proceed to the Madreporite This is a very nu merous tribe, and is accordingly separated into subdivisions by Linnxus and other naturalists. That one which resem bles a top, commonly called turbinata, is only known in the fossil state. The Madrepora porpita, or shirt-button madreporite of English collectors, is another of this genus, which, like the former, is common in many limestones ; and both these come under the division in which there is only one star. Of the more complicated, the Madrepora labyrinthiaca, or one resembling it, is sometimes found in the fossil state, being commonly known by the name of brain stone, from its general resemblance to the convolutions of that organ. Other specimens have been found, of a kind resembling the retepora ; very noted among quarrymen from its similarity to a honey comb. The M. truncata is ano ther species in this genus, very remarkable for its prolifer ous structure, and for the very beautiful disposition of its as is the stellata ; both of these found in the fossil state : but, as we dare not extend this list to the numerous kinds which have been found, we shall only further re mark, that the presence of these fossils often gives rise to very beautiful marbles, and that they are also occasionally found silicified by flint and chalcedony ; in which case they are cut, like agates, for ornaments.