NOTES AND ILLUSTRATIONS.

NOTE I. p. 33.

WE subjoin the following remarks on the strata round Edinburgh, from our Geology of the district.

"Another subject of inquiry is the relative age of the trap rocks; and to decide this, we think we have sufficient data. From the entire absence of trap debris in the sandstone of the coal measures, and, on the other hand, from the uniform presence of mica there, we are entitled to conclude that granite or gneiss rocks furnished the materials of this extensive deposit ; and that consequently, no trap rocks existed in the vicinity up to the period of the last carboniferous deposit. In the more superficial strata, within a few hundred yards of the surface, we begin to have evidence of trap.

That the trap rocks have been the agents in the elevation of the carboniferous strata, is also evident; for these disrupted strata rest upon the trap; and on the south side of Arthur's Seat, portions of limestone and sandstone still remain, which have been carried upwards.

Another question arises: Are the trap rocks all of one age, or are they of different epochs? There appear to be two facts which indicate a difference of age of

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these rocks: First, The different character of the trap placed in juxtaposition, and the marks of disturbance by which the older was affected by the intrusion of the subsequent; Second, The appearance of trap debris, and rounded masses of these rocks imbedded in strata which have been elevated by a subsequent eruption of trap.

If we might form any conjecture, however, from the quantity of this debris accumulated, the period between the first and last eruption of trap must not have been long certainly a very short period, indeed, compared to the time necessary for the deposition of the coal

strata.

The next inquiry is- Were the trap rocks elevated under the water of the ocean, or after the plain of MidLothian became dry land? The facts stated immediately before, will shew that the first eruption of trap, at least, must have been while the waters of the sea still flowed over the spot, and that the ocean continued to flow for some time, by which the trap debris was formed, and many of the large boulders probably carried to the situations where we now find them.

Another fact corroborative of this is, the amygdaloidal state of the vesicular trap of Arthur's Seat and the Pentlands, which must have been owing to a deposit of matter held in solution by a fluid in which they were immersed, subsequent to their eruption in a porous lavalike form.

That dry land, however, almost immediately succeeded the last elevation of the trap rocks, is apparent from the state of the diluvium which lies immediately above, and which appears to have been at once deposited, before the sharp edges of the rocks had time to be worn down,* and which diluvium has ever since remained undisturbed and unmixed with any marine substances which could indicate the presence of an ocean. To this diluvium has

* This is seen at Niddry quarry, and elsewhere.

succeeded, at no long interval, the present soil, with its present vegetables and animals.

The most remarkable and unaccountable circumstance accompanying the last elevation of the trap, seems to have been a total and abrupt change of the whole country. The animals and vegetables that covered the, former soil, and stocked the former seas and rivers, appear to have been entirely destroyed, and their remains overwhelmed and buried in the great convulsion of nature. Not only had their destruction and extirpation been complete, but the whole constitution of soil and climate seems to have been so altered, as to preclude the possibility of their again existing, had a remnant even been saved. From all we can ascertain of the structure, both of the animals and vegetables of this carly period, they bear a nearer analogy to those of tropical climates than to any that exist in the temperate regions of the globe.

We here in vain look for any thing intermediate between the animals and vegetables of the carboniferous era and those of the present. The same kind of coprolites are found in the alluvial clay as in the low-lying shale; and in the highest beds of the coal measures, the same leaves snd trunks of vegetables are in as great abundance as in the seams 3000 feet lower.

Immediately, too, after this convulsion, the sedimentary deposit of sandstone appears to have ceased. No more vegetable remains, either, have been accumulated in those singularly alternate layers which seemed to mark a periodical overflow of some huge river, or some other unknown modification of transporting currents. Not only had the catastrophe produced a local change, but it had extended to all the region then in connection with this part of the country.

In the alluvium, we have already remarked that many rounded masses or boulder stones are to be found. These consist of fragments of all the rocks in the neigh

bourhood, together with some of granite, gneiss, and porphyry, that must have been transported from a distance of not less than fifty miles. The position of these

stones, relatively to the masses from which many of them have evidently proceeded, indicates decidedly a current flowing with considerable force from west to east. Masses of sand, too, accumulated in various places, exhibit that waved stratification which evidently proves the existence of a former current. In the diluvium around Edinburgh, few or no traces of the remains of mammalia have been found; but to the westward, about Alloa, and in Stirlingshire, the ivory tusks of the elephant, and the horns of ruminating quadrupeds allied to the elk, have been from time to time discovered. All these circumstances, joined to the appearances already pointed out at Burdiehouse, lead to the conclusion that land has existed to the westward, that from thence has proceeded one or more large rivers, and that the situation where Edinburgh now stands may have been the bottom of some estuary."

Niddry quarry is about two miles south-east of Edinburgh, and is formed by the tilting up of the northern edge of the Mid-Lothian coal measures, by means of the greenstone rocks, which intersect these deposits. The strata, as seen in this section, are nearly vertical, and consist of alternate layers of shale, sandstone, and seams of coal.

Immediately above the strata thus elevated, is superimposed the diluvium c, c, a mass of clay, five feet in depth, with fragments of sandstone and boulders, of the same nature as those which prevail in the surrounding district. The sharp unworn edges of the sandstone and shale, exhibiting the same appearance which they must have borne when newly severed from the connecting layers, proves that the superposition of the diluvial matter immediately succeeded this elevation; and the

a, a, Sandstone. b, Shale. c, Diluvium with boulders. d, Present soil.

mass of diluvial matter which penetrates about two feet into the fissure at e, evidently shews that no denuding current had swept away any newer strata which might have been deposited above; for such newer strata, if it had existed, must have pre-occupied this fissure.

In this same diluvial covering, at Clifton Hall, near Falkirk, fifteen feet below the surface were discovered some years ago, two tusks of a fossil elephant, and several other fragmentary remains of mammalia are occasionally, though rarely, met with. Now, the question is, Was the elephant a contemporary of, the diluvial clay in which its tusks were imbedded? and was this diluvium contemporaneous with the coal measures above which it lies? If these questions are admitted in the affirmative, then we have the fossil elephant a contemporary of the coal formations. But we have the megalichthes, and many other species of extinct fishes and shell mollusks, in the coal and subjacent limestone, which would also, in this way, claim a contemporary era with the mammoth. :