no easy matter to distinguish them on this Contipent at least. They have all orignated in the same cause, differing only as to its antiquity and activity. The exception alluded to, embraces certain recent or modern alluviums, which are now forming in estuaries, on the sea shores, and at the mouths and on the banks of inland rivers. No example of the first two actions, of course, come under our present notice; but as we descend towards and through the Gulf

, they may be seen constantly in unceasing operation. The St. Charles and St. Michel rivers afford good instances of the two last; and the Vacherie, in all probability, owes its existence to the united action of these two confluent streams. Pursuing a course nearly at right angles to each other, they traverse for some distance, before joining the St. Lawrence, on the way from their western and northern sources, a country covered with loose or plastic, silicious or alluminous deposits, in which they sometimes form deep sections, and in which, in their progress, they are constantly producing a change, either in the way of abstraction or addition,--stealing from a salient angle what they restore at a re-entering one. Now, it is precisely such deposits as form the original sections of the portions of these rivers we allude to, that puzzle the Geologist who wishes to determine whether they are to be considered Alluvial, Diluvial or Tertiary. From the recent or modern alluvium just described, they are easily distinguished, as well by the superior relative altitude at which they are found, as by the fact of their having long ceased to increase, the cause of that increase being no longer in action on the spot where they are found. But it is quite different as regards the distinction between the more ancient deposits we are discussing ;-here is no well

[ocr errors]

defined geological horizon; they often seem to mirage as it were, or merge one into the other.

The structure of these deposits may be best seen on the St. Michel and Beauport rivers. The former presents us with sections of sand or loam bedded on clay, sometimes containing drift wood and boulders, and assuming, occasionally, a stratified arrangement. The latter discloses embaying cliffs and heights of plastic clay, surmounted by sandy deposits, and in one remarkable instance, by an entire bank of marine shells, whose greatest depth is from 25 to 30 feet. In many parts of these cliffs stratification is a distinct feature, and towards their bases it assumes the appearance even of that of the indurated clay slates of the neighbourhood; but the ease with which its hardest portions may be moulded under the action of the fingers and moisture into any form, is a sufficient distinction—a distinction which has probably an analogous origin to that which exists between loam and the brick which is made from it. This alluminous substratum we are disposed to class among Tertiary formations, while the loose and more silici.. ous materials above, including the fragments of primary aggregates imbedded in them, we would reer, in geological strictness, to the ancient alluvium, not but what (and hence arises the difficulty of distinguishing them) the tertiary formations are also of an alluvial character, and may, in fact, be considered the most ancient of alluviums, (the Secondary and Transition rocks, which, for the most part were once so, having undergone geological changes which have removed them from that class, the most striking of which changes in general is the degree of induration they have acquired and their fixture in water.) But some Geologists attempt, not always very success

fully, it must be confessed, to establish a difference between the tertiary formations and the ancient alluviums: It is much easier to conceive the difference than to describe in what it consists. However, the same analogy exists between them as between the ancient and recent alluviums, the one being often caused by the breaking up of the other.

The bank of shells we have described as overlying in one spot the plastic clay to the depth (a maximum) of 25 or 30 feet, consists of an intermixture of silicious sand, and for the most part, bivalve shells, stained here and there with the peroxide of iron. The shells are usually bleached and brittle, sometimes exhibiting a pearly nacre, and always, we conceive, in the possession of a portion of their animal gluten. The bivalve shells appear to be the following, set down in the order of their abundance :

Hiatella (arctica), (in the largest proportion.)
Tellina (?)
Mya (truncata.)
Mytelus (Borealis ?)
Pecten (?)

Terebratula (psittacea.)
Among univalves have been found-

Buccinum (undatum ?)

Scalaria (rare.) A Mutivalve, also the Balanus tintinnabulus, in fragments, is also common.

It is remarkable in this bank, that the two largest genera of shells found in it, viz.: the Mya and the

Pecten, occupy in layers, the lowest portion of it. It has also been observed, that the clay here, though supporting this calcareous burthen, does not in the least effervesce with acids.

If much diligence were used in the research, it might be possible to find, perhaps, as many more as those enumerated above, differing from them either in genus or species; but these are all we could collect, after several examinations of the bank; and having little information on the subject ourselves, they have been submitted, in the first instance, to the Countess of Dalhousie, and subsequently to Mrs. Sheppard, of Woodfield, -two females whose refined tastes have led them to a successful cultivation of more than one branch of Natural History; and to one or other of these ladies we are indebted for the above quoted names. Mrs. Sheppard observes on the singularity of finding a fresh water shell (melania) mixed up with the others which are exclusively of marine origin. The fact would seem to imply, that when this bank of shells was deposited land was not far off.

The commonest of these shells, the Hiatella and Tellina, have been traced from hence to other places in the neighbourhood, even to Charlesbourg and Indian Lorette ; but they are far from occurring in such profusion as here. The fact appears to be, that the bank suddenly wedges out to a very thin stratum or layer.

Whether this bank is to be considered a member of the Tertiary formation, the Pliocene of Lyell, for instance, or an ancient alluvium, in the strict geological interpretation of the term, we cannot decide.

Captain Bayfield, R. N., is, we believe, about to transmit to Mr. Lyell, a collection of specimens from

this locality, which will, no doubt, enable the latter to afford us that correct information on the subject which he must possess, from having so deeply studied it in connection with its European developements; in the mean time, we recommend a visit to the spot to all those who are fond of casting back a retrospective glance to the days which have left no other records behind them than such as are to be found in the materials composing these ancient deposits. The feelings and thoughts which such a visit will excite may be somewhat vague; but they will scarcely fail to prove both interesting and instructive.

Before we bring this subject to a conclusion, something must be said of a portion of the alluviums, which, as yet, has obtained only an incidental notice. It is manifest that the fineness or coarseness of the deposits which accompany an alluvial action, must depend upon the force of the latter. Where, in the present day, this action has been moderate and continual, we often find deep deposits of the finest materials. In places, on the contray, liable to a violent rush of waters, these materials are of the coarsest description. Apply this remark to some of our ancient alluviums, and it will appear that they could only have been deposited by the action of a deluge, either rushing suddenly to its climax or as suddenly subsiding from it, and to such the term diluvium is applied. They are to be found at all levels—sometimes encumbering the surface of the ground in large rounded masses (boulders,) or as a coarse gravel, contrasting usually both mineralogically and geologically with the fixed masses of rock they overlie.

To satisfy one self that water has been in general the transporting cause, we have only to turn our eyes to the beds of some of our rivers, in which,

« ForrigeFortsett »