XVII. to one general Originator, and linking all sentient LETTER things into one great family of related fellowcreatures.87 earth, with a glutinous hinge, so dexterously, that it fits exactly to the space, opens easily, and closes of itself when the animal has entered. A few small holes are pierced in this door, on the side opposite the hinge, to enable the spider to hold it fast with its paws, in case any thing was trying to open it. Bull. Univ. Ap. 1831, 132. 87 A passage on the Locusts, in Captain Hall's Fragments, will afford a specimen of the innumerable quantity of Insects that are living on the earth. Capt. Beaufort told him, that when at Smyrna in 1811, he had an opportunity of forming a rude estimate of a flight of Locusts, then drifting from South to North. The consul's messenger to Sardis rode 40 miles before he got clear of their moving column. It was inferred, from observations made with a pocket telescope, that the height of the column could not be less than 300 yards; and the rate of its passing was not slower than seven miles an hour. This continued for three days and nights, apparently without intermission. As these insects succeeded one another at an average distance of not more than three inches, and were about one foot apart above one another, it was computed that their lowest number in this enormous swarm must have exceeded 168,698,563,200,000, or, in English numeration, 168 billions 698 thousand 563 millions 200 thousand Locusts. Hall, Fr. 2d Series, v. 3, p. 84. LETTER XVIII. ON THE FOSSIL REMAINS OF ANIMALS FOUND IN THE MY DEAR SON, LETTER THE Other Topics which remain to complete my obXVIII. jects in these LETTERS will not allow me to detail to you all the facts that ought to be known and considered with respect to the Fossil Remains of Animals which the rocks and strata of our Earth contain, and which human labour or curiosity has disclosed, in modern times, to our view. To do full justice to the subject, the right theory of our GEOLOGY ought to be first well settled. But the diversities of opinion which still prevail, show that this is impossible at present. We know enough for ingenious speculation, and also for hesitation and doubt; and we are from time to time acquiring more elucidating knowlege ; which is leading the intelligent inquirers, who are pursuing this interesting subject, to better reasoning, and to more just conclusions. But we seem to have arrived at that point in which further discoveries from our Mineralogical investigations become necessary, before any true system can be established as to the formation of our Globe. Scientific men have traced its constituent substances to fifty or sixty simpler bodies, which at present rank as elements, because they are not yet further decomposable; and XVIII. these appear to have constituted our primordial LETTER rocks. But there are abundant reasons for surmising that they are not the primitive elements of material nature; and therefore until they can be resolved into the particles or substances which are so, we shall not attain those perceptions of the original composition of our multifarious Earth, which will present the deciding and satisfactory truth. We must know what Silica, Alumina, Magnesia, Lime, Carbon, Iron and the other metals and primitive components of the Minerals intrinsically are, before we can accurately discern the process of the succession, the causations, the agencies, the laws, and the principles, on which the Primary and Secondary masses were originally formed. The acquisition of this further information would have been thought impossible in the last century. But human sagacity and industry are now exploring what is unknown, so perseveringly and so successfully, that every month may bring us the information, that some diligent Analyst, in some country or other, may be drawing from Nature those great secrets of her primordial chemistry, which have hitherto been impervious and inaccessible. In this state of unsatisfactory ignorance and uncertainty, it will be sufficient to notice the Organic Remains which have been disclosed, with a few brief remarks on the subterraneous structure which contains them. The ground we tread upon, and from which vegetation now springs, is not the primitive surface of the Earth. It is the upper part of the last series of strata which have been deposited upon and around it, and which is now most commonly denominated the TERTIARY formations. By this term, the series of subterraneous beds, down to the chalk rocks, are XVIII. LETTER named and known; and they are manifestly more recent than the masses below them.' These are considered by many, and, I think justly, to have been formed at the period of the Deluge, from the fragments and ruins of the Earth's previous surface, amid the concussions and perturbations of that general catastrophe. But, however this be, these Tertiary beds are clearly distinguishable from the more ancient, and are treated of as a class by themselves, different from what preceded them in position, appearance, fossils, and composition." Below these occur another great series of various rocks, of a stratified and sedimentary nature, which have been called Transition, or Intermediary, and Upper and Lower Secondary. But to all these, the general term, Secondary, as marking one great outline of chronological distinction, from both the ear 2 ' Conyb. Geol. Introd v-vii. M. de Serres, Geogn. p. xcii. ' M. Dufresnoy calls the beds that have been deposited on the extensive chalk formation Terrains Tertiaires.' Bull. Un. 1831. No. 4, p. 38. . . . . We find a mantle as it were, of earth and sand indifferently covering all the solid strata, and evidently derived from some convulsion which has lacerated and partially broken up those strata, inasmuch as its materials are, demonstratively, fragments of the subjacent rocks, rounded by attrition.' Hence they must be assigned to the last violent and general catastrophe which the Earth's surface has undergone.' Mr. Conybeare, therefore, calls them Diluvial. Out. Geol. p. 4. 3 M. Marcel de Serres' Geognosie des Terrains Tertiaires,' 1829, is devoted to this class of the Earth's strata, and to their animal fossils. Transition, or intermediate rocks, cover those of the primary class, and are distinguished as the lowest rocks in which the fossil remains of animals or vegetables are found.' Bakewell Geol. p. 124. ... .In these he includes the Slate, Grey Wacke and Mountain Limestone. His Upper Secondary Class comprises the Magnesian Limestone; Red Sandstone; Lias; Oolites; Sand; Clay and Chalk Rocks (p. 236;) naming the Coal formations his Lower Secondary.' 146. lier and the later, and as embracing the whole series, LETTER seems to be very fitly applicable. This leaves that of XVIII. Primary, or Primordial, for those crystalline and other masses which are found beneath them, and on which they rest, and beyond which, human knowlege has not penetrated. These are, the Granite, Gneiss, and Mica Slate Rocks, with their subordinate resemblances. All these are mainly formed of the same materials, in different proportions and modifications; Quartz, Felspar, and Mica; with some occasional additions of a few other particles: and they are found in all regions of the Globe, and of the same composition.' In these primordial rocks no organic remains have been seen; and from this circumstance it is reasonably and generally concluded that they were formed before animal or vegetable life began. It is in the Secondary rocks, those that were deposited or composed after the Primary ones were consolidated, and before the Tertiary strata accrued, that fossil exuviæ first occur. The SECONDARY formation consist of new rocks, formed from the fragmentary ruins or disintegration M. Marcel de Serres accordingly attaches the denomination of Secondary to all these classes; distinguishing them into the three modifications of Upper, Middle, and Lower.' Geog. p. xcii. . . This simplicity seems preferable, in a large outline of the subject, to M. Al. Brongniart's numerous minute divisions, with a long train of new Greek-derived names. • Bakewell's Intr. Geol. p. 84, 5. Al. Brongn. Ecorce du Globe, p. 340, 1. 76 7 With the Granitoid groupe all the earth is covered.' Al. Brongn. p. 342....Geologists have observed, that mountain masses display every where the same rocks, the same assemblage of Mica, Quartz, and Felspar, in Granite; of Mica, Quartz, and Garnet, in Mica Slate; and of Felspar and Hornblende in Syenite.' Humboldt's Geogn. Ess. p. 4. |