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tion. At a maund an acre, they would yield 7,600,000 lb., which is equal to one-sixth the entire consumption of Eng. land. If the application of capital to this object receives a sufficient impulse, we might, in the course of ten or twelve years, have the gratification of seeing England draw the largest portion of her supplies from this country, and a new trade of L.3,000,000 or L.4,000,000 sterling a year, grow up in India, stimulating industry and diffusing plenty, and increasing the mutual benefit which the two countries derive from each other. The multiplication of the supply in such abundance would also tend to reduce the prices at home and throughout the world, and thus augment the consumption. Nor must we forget the great impulse which these tea plantations—a large proportion of which would necessarily be fed by British capital-must give to steam communication between the two countries, and the additional importance they would impart to the establishment of a railway from the port of Calcutta to the north-west provinces.
But the country itself would reap no small advantage from the facility of obtaining supplies of tea at a reasonable rate. The natives of India are partial to this beverage, and the use of it will be extended in exact proportion to the degree in which it is brought within their means. A rupee and a half a seer, at which rate Dr Jameson calculates that the cultivation will yield a profit of nearly two hundred per cent., would place the Kemaoon tea within the reach of the whole body of the middling classes; and the demand for it, in the country itself, would be sufficient to furnish the highest encouragement to perseverance, independently of the European market.-Friend of India, Serampore, Feb. 4, 1847.
On the Occurrence of Stones on the surface of Glaciers, as con
nected with Glacier Stratification. In a Letter to Professor JAMESON by M. E. DESOR.
New Haven, 15th May 1847. SIR, I have just seen, in the fine library of M. Silliman, the 83d Number (vol. xlii.) of your Journal, containing two new letters upon glaciers by Mr James D. Forbes. The facts
reported have so much the more interest in my eyes, as they agree, in a very satisfactory manner, with the observations made during the last year upon the glacier of the Aar, and reported in the new work of M. Agassiz upon the glaciers.*
It is easy to perceive, in reading over the most recent publications upon the glaciers, that the opposition between the different theories tends constantly to disappear, in as much as facts take the place of speculation ; for there can be no doubt that the different physical laws, as gravitation, plasticity, expansibility, which have been insisted upon in a too exclusive manner by authors of different theories, have each some influence upon the mechanism of the glaciers.
Nevertheless, there are some points which are still viewed very differently in the different systems, and especially those concerning the structure of the glaciers. M. Agassiz, as you know, makes a distinction between the strata, which are the result of the annual deposit of snow, and the blue bands. The first, according to him, extend entirely through the glacier, and very often sand and fragments of rock are found between them. These are the so-called dirt bands of Mr Forbes. The blue bands, which are so frequent in the middle and lower part of the glacier, have not the same importance, being merely the result of superficial fissures parallel to each other, and usually agreeing with the general direction of the strata.
Mr Forbes, on the contrary, looks upon them as the consequence of the unequal rapidity of the movement in the different parts of the glacier. He mentions, in his 12th letter, a fact concerning the glacier of La Brenva, which, according to him, would be an “experimentum crucis” in favour of his theory. The glacier of La Brenva, in the valley of Chamouni, like most of the glaciers of the Alps, has increased very rapidly of late years. Mr Forbes has noticed that the blue bands are the most striking in the most advanced portion of the glacier, at the part below the promontory marked B in his figure (p. 100 of volume xlii. of this Journal). According to him, this is owing to a “ longitudinal tearing,” and
* Systeme Glaciare, ou Recherches sur les Glaciers actuels, &c., with an Atlas, 1847 ; not to be confounded with his former work, entitled, Etudes sur les Glaciers, 1840.
the movement would be facilitated by the numerous fissures occasioned by this tearing.
At any rate, I must say that this splitting supposes a degree of rigidity entirely at variance with the theory of semifluidity, and that it could hardly be accounted for, éven by the theory of expansion. There is, I think, a much more simple way of explaining this phenomena; it is, that the glacier, after having passed the promontory, where it was somewhat compressed, comes out into a freer space, where it is able to expand, and the laminæ, being seen projecting one beyond the other, like the leaves of a book when bent, become more striking. The same thing takes place in the glacier of the Rhone, where the laminated structure is more striking below the fall than above; and similar effects may be observed in all the lateral expansions in the glacier of the Aar.
I come now to another point,—the appearance of stones on the surface of the glacier. It is a subject upon which most singular opinions have been expressed, and which appears, in fact, at first most enigmatical. When we examine attentively the debris on the surface of one of our large glaciers, we see frequently masses and tracks of stones, which commence in the very midst of the glacier, without any apparent connection with the mountain slopes from which the lateral and medial moraines proceed. We know, also, that the mountaineers pretend that the ice of the glacier is perfectly pure, including no kind of foreign body in its interior; and, in fact, it is true that we find very rarely any foreign body in the walls of the crevasses. Nevertheless, these are occasionally found; and therefore I agree entirely with Mr Forbes in thinking that all the stones lying on the surface of the glacier “must previously have been imbedded in the virgin ice.” The question is, how did they reach the surface ? Mr Forbes, referring to the glacier of the Rhone, which is nearly destitute of stones in the upper part of its course, whilst he says “ they begin to appear at the surface at the
erminal slope,” has proposed a very unexpected explanation to account for their extrusion, which he has illustrated by the diagram, No. 83, Pl. II., fig. 7, of this Journal. He supposes
that the stones "are actually introduced into the ice by friction at the bottom of the glacier, and forced upwards by the action of the frontal resistance which produces the frontal dip of the veined structure, and that they are finally dispersed on the surface by the melting of the ice."
There is scarcely any geologist conversant with the phenomena of the glaciers, who could be satisfied with this explanation. I shall endeavour to shew that the appearance of stones at the surface is obviously the consequence of the primitive stratification in the upper parts of the glacier.
Let the diagram be the longitudinal section of one of our large glaciers.--the Glacier du Rhone, for example. Like all the large alpine glaciers, its greatest thickness is probably at its beginning ; but, in consequence of the annual melting, it becomes more and more reduced as it advances. In order to supply its place, a new stratum of snow is annually deposited at its origin, and in the mean time a certain quantity of rocks fall down on it from the neighbouring mountain slopes x. The next winter this layer, with its debris, will be covered by a new stratum ; and if there were no melting, and if the motion were equal in all the parts of the glacier, this debris would remain buried (below the dotted horizontal line), and be for ever concealed in the interior of the glacier. But we know that a certain amount of ice is melted every year from the surface of the glacier, and in consequence of this, the debris become by and by discovered. The first will appear at the outcropping of the stratum a. Little farther below another boulder will come forth out of the layer b, another, again, out of the layer c, and so on, till they become so numerous that they form regular tracks. Beautiful examples of this appearance of stones and moraines are shewn in the map of the Glacier de l'Aar, in M. Agassiz' new work, to which I refer for more ample information on this subject. This appearance affords us, after all, the most striking evi
dence that the primitive stratification is not obliterated, as Mr Forbes has maintained, but that it is preserved through the whole mass of the glacier. They shew also, better than any discussion, how little analogy there is between the structure of the glacier and that of a lava stream.
Barton, 30th May. Postscript.—Concerning the motion of the glacier during winter, you will see that the results of Mr Forbes, as stated in his 14th letter, agree, in a very satisfactory manner, with those obtained by M. Agassiz and myself on the glacier of the Aar. In this respect, as in many others, the Glacier of the Aar is not at all an exceptional one, but is governed by the same laws as those of Chamouni, and all large glaciers in general.
On the Manna of the Scriptures. Dr Wright* describes a substance he met with, under the name of manna. We found, says he, “ in one part of the mountains (probably on the return route) great quantities of a sweet substance found on the leaves of certain trees, generally the oak and gall-nut tree, and which is called gezza in Koordish, and manna in Syriac, and perhaps honey-dew in English. It forms on the leaves in such abundance, that, when they are dried and pounded, it comes off in scales, and is collected and used as an article of food. When melted and strained, in order to separate the crumbled leaves, it is very delicious, and is eaten by the people often in preference to honey. In the summer it is collected in large quantities, and put up for winter use. Often, as we were riding along among the trees loaded with it, we found it pleasant to break off the branches and lick the leaves, which were so coated with it, that in a very few minutes our appetites were satisfied. There is a species of willow growing in the water-courses in Persia, on which this article is sometimes found; but we have never seen it there in such abundance as in the Koordish mountains."
The term manna ordinarily refers to the well-known product of several species of Fraxinus, " that grow spontaneously in Italy and Sicily, and very probably in all the oriental Mediterranean region,” and which is used for medicinal purposes.
Substances which resemble this in form, or taste, or mode of production, are also called by the same term, which in every case, therefore, needs defining. The gezza was observed in June, and, from Dr Wright's account, we infer it was a semifluid exudation upon the leaves of certain trees.
* Dr Wright is a member of the American Mission, at Oroomiah, in Persia.