Geological facts; or, the crust of the earth, what it is, and what are its uses

by W. G. Barrett

To this glowing description we might add what we ourselves have witnessed on the coast of South America, where the great Amazon, the Orinoco, and the Essequibo, roll their mud-laden waters into the Atlantic, and form vast accumulations of alluvial deposit all along its northern coast; indeed, the coast line of all the Guianas of South America, averaging some five to ten miles in width, and at least 1,000 miles in length,—Venezuela, British Guiana, Surinam, and Cayenne,—are nothing more than the deposit formed at the base of the mountains by these and other rivers of smaller note. Buried in this mud are pebbles, trunks of trees, animal remains, and so on; and if these in process of time should be elevated and afterwards hardened, or submerged and pressed into clayey slate or sandy stone, the fauna and the flora of these deltas would then be brought to light, just as the leaves of plants are exhibited between the pages of a botanist’s collecting book.

In some such method as this was once formed a delta, now constituting the Wealden formation in our own country. What is now the south-east of England, including the Weald clay, the Hastings sand, and the Purbeck beds of limestone and marls, in short, the greater part of the counties already named, with part of Dorsetshire, was once the delta of a mighty river, that so long and so uninterruptedly flowed through this then uninhabited part of the planet, that its accumulated deposits average 1,000 feet in thickness. We have but to pause over those words—one thousand feet thick;—once mud, or rather fluviatile deposits of mud and sand, a thousand feet thick in order to receive fresh evidence of the high antiquity of the globe, and of the recent creation of man. We have but for a moment to remember that these deposits consist of innumerable layers of mollusks and crustaceans, a prodigious accumulation of the bones of reptiles and fishes, and of the trunks, branches, and foliage of a long extinct vegetable world, all quietly brought down by “the rivers of waters” of that era, and carefully and without injury deposited in what were then the bottoms of bays or the rising land of deltas, in order to appreciate the evidence which this one deposit alone affords of the immense period of time occupied in its accumulation.

Our next section, the cretaceous division of the secondary rocks, presents us with an exclusively marine deposit. The Wealden, as we have said, is a fresh-water deposit. “Many a long and weary journey,” says Dr. Mantell, “have I undertaken to examine the materials thrown up from a newly-made well, or the section exposed by recent cuttings on the roadside, in the hope of obtaining the data by which this problem is now completely settled.” The data referred to are such as these—the absence of all ammonites, encrinites, corals, terebratulæ, and other marine organisms, which form so large a portion of the cretaceous and other sea deposits.

Here, again, we may anticipate future remarks. It may be thought—by some it has been roundly asserted—that these fossils were placed in their present situations by the deluge. Without entering into the theological question, as to the universality or partiality of the Noachian flood, although, as we shall hereafter see, there is but one opinion on that subject held by our best geologists, namely, that the deluge recorded in the Bible was simply the subsidence or submerging of so much of the earth, and no more, as was then inhabited by man, and that so partial and so limited was its character, and so brief its duration, compared with those vast geological epochs we have been considering, that there are no traces in nature of that event at all, i.e. that we have no one single fossil that can be referred to that event,—without, we repeat, entering upon the investigation of this subject, which will be done in a subsequent part of this volume, we would merely remark, in reply to this absurd notion, that the Wealden is evidently an alluvial, and not a diluvial formation; and as these terms are so frequently used as if they were synonymous, we shall venture upon our old habit of explanation. An alluvial deposit is formed by the ordinary, but a diluvial deposit by the extraordinary action of water. Thus all the straths and carses of Scotland, and our English dales or dells, (may not the remote etymology be delta?) are all of alluvial formation; while, as owing their origin to diluvial, or the violent action of water, we are to ascribe the heaps of rubbish, gravel, sand and boulders, that are found in firm compact together.

Thus, if we take a basin of water holding a quantity of earthy matter in solution, and place it on a quiet table, and allow the earthy matter gradually to subside, that which is found at the bottom of the basin is an alluvial formation, deposited by the quiet and ordinary action of water.

But when, as sometimes here in Royston, a sudden and heavy rain occurs, when for a while “the windows of heaven” seem opened, and the surrounding hills pour down their rushing streams through the town, filling, as unfortunately they do on such occasions, the cellars of our neighbours in the bottom of the town, with sticks, stones, flint, gravel, bits of chalk, paper, bones, cloth, and a variety of intermingled sundries too numerous to mention, and all huddled together in wild confusion, then is formed in such ill-fated cellars a diluvial deposit, occasioned by the extraordinary action of water.

Now, the Scripture flood (and we may be allowed to say, we are not trying to explain away the fact of the deluge,[^[100]] nor to weaken the strength of the Mosaic narrative, but the very contrary) was a most extraordinary event. Not only were the “windows of heaven opened,” but the “fountains of the great deep” were broken up, and if it had left any traces of its action, they would have been of a heterogeneous and diluvial character; whereas in the Wealden, as elsewhere, the fossils occur in the most orderly and quiet manner, preserving in many cases those exquisite forms of beauty which distinguished them during life.

Without entering more fully into details of the fossil remains of this period, we shall conclude this chapter by a reference to one of the vast saurians whose remains have been disinterred from the Wealden. Many years ago Dr. Mantell discovered, in a quarry at Cuckfield in Sussex, a tooth, which he took up to the Geological Society of London; it was altogether unlike any tooth he had hitherto found, but yet it was so common, that the quarrymen had broken many of them up to mend the roads. The most eminent geologists of the day were puzzled extremely with this tooth. One thought it belonged to a fish; another, that it belonged to an unknown herbivorous mammal; and a third, who was right, that it belonged to a herbivorous reptile. Sir Charles Lyell was at that time about to visit Paris, and the tooth, and that alone, was shown to Cuvier, who at once pronounced it to be the tooth of a rhinoceros. In the process of time other fossil remains were found, portions of jaws, cervical, dorsal, and caudal vertebræ; and on Cuvier seeing these, with the magnanimity of a truly great mind, he frankly avowed his error, and said, “I am entirely convinced of my error in pronouncing it to be the tooth of a rhinoceros.” Shortly after, Dr. Mantell was fortunate enough to procure the skeleton of an iguana,[^[101]] and he found that the fossil teeth found in Tilgate forest bore a close resemblance to the teeth of the iguana. The teeth of the iguana were found to be small, closely set, and serrated like the edge of a saw, not so much for crushing victims, as for champing and grinding its vegetable food; this corresponded precisely with the fossil teeth found, and after long and careful deliberation, the name given to this crocodile lizard, and the name which it retains, was Iguanodon, or the reptile with teeth like the iguana.

The probable size of the Iguanodon was thirty feet in length, though probably some exceeded these enormous proportions. Seventy species have been discovered in the quarries opened at Tilgate forest; and this gives us some idea of the conspicuous part these mighty creatures once played in the eras happily before man was an inhabitant of this planet. Why these remains should generally be found in the same locality we cannot certainly tell, though the previous extract from Alison may shed some light on this curious fact; but it appears beyond doubt that particular spots were selected by these beasts as hospitals and dying places, where, undisturbed by their enemies, they retired to die unseen.

The drawing on page 195, representing the restored fauna of this period, that is, inclusive of the Lias, Oolite, and Wealden formations, will not only illustrate our previous remarks, but enable our readers thoroughly to appreciate the following vivid description of the life of that remote era, which we do not like to abridge. Should any feel sceptical as to whether there were ever such “goings on” in this globe of ours, especially in our eastern counties, now the resort of tourists and invalids having no dread of such creatures before their eyes, we ask them not to reject all this as fable until they have gone to the British Museum, and in Room 3, and in Wall-case C, they will there see some of the magnificent specimens, obtained by Dr. Mantell, of these extinct deinosaurians.[^[102]] On reading this description, it seems quite justifiable to congratulate ourselves upon the era in which we live. Strange forms and monsters vast have been in the old time before us, and their disinterred remains teach us again and again the good and wholesome lesson of the king of Israel, prefixed as a motto to this chapter.