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the top of the stems, or above water, these stems can not help much in the process of purifying the muddy water. Yet it is true that it becomes clear towards the interior of the marshes, but only as fast as the current becomes insensible or the water still.

Mr. Lyell has been quoted as authority for many assertions for which he can scarcely be held accountable, or at least for the conclusions which are drawn from them. Thus the new theory of the formation of the coal tries to find support in a geological assertion of the celebrated English author, an assertion that I do not recollect to have read in any of Lyell's works and which would truly show too much of ignorance of the paleontology and even of the strata of the coal measures. It is this: "In the sandstone of the coal formations, it is customary to find trunks of trees, but only trees, no small branches, leaves or tender parts. And these trunks are observed to be mostly pines, highland trees, while the trunks of the coal seams proper are Sigillariæ, Lepidodendra, Calamites, swamp trees, &c. From this, the new theory concludes: that the trunks are the remains of drift timber brought by the river from the high lands.-As if the sea could not and did not float timber as well as a river!

But it is not with the conclusion that we have to deal now, but with the assertion, erroneous in every point.

1. The trunks of trees are by far more rarely found in the sandstone of the coal than the small fragments of leaves, branches, &c. Some strata of sandstone, the Mahoning sandstone and oth ers of the low coal measures, are sometimes entirely blackened by those small fragments of plants so bruised that it is scarcely possible to identify any species. This is not a local appearance; but it is observable in the whole extent of the coal-fields generally on the same stratum of sandstone. This shows a rapid movement of the sea, which sweeping with impetuosity upon the peat bogs of the coal, washed away part of the decomposed plants and peat bogs and mixed them with the sand.

2. Representative species of the Pine family have scarcely been found in the true coal measures. In the family of the Cupressinee which has more than sixty species of fossil plants distributed in twenty genera, there is not a single species belonging to the coal epoch. In the family of the Pines which has at least one hundred and fifty fossil species known, distributed in twelve genera, there are only thirteen species which have been referred to the true coal measures. Two of these, Peuce Hugeliana Ung. and Peuce australis Ung., belong to uncertain formations of coal of Van Diemen and Vanguroe Islands. Of two other species, one, Dadoxylum Beinertianum (Endl.) belongs to the limestone (not to the sandstone of the transition epoch), the other Dudoxylum Sternbergii Endl. was wrongly ascribed to the coal and be

longs to the Miocene of Haering in Tyrol. A fifth species, Pinus anthracina Ll. and Hutt., is a cone which was found in the shales of England. There are then only eight species of the pine family which have been found in England, in a bed of sandstone referred to the upper coal measures and described by Witham.

Admitting the position of this sandstone as true, though it is most remarkable that the remains of the Pine family should have been found in the coal measures of England only, there has been found in the sandstone of the coal measures 4 species of Stigmaria, 15 species of Sigillaria, 10 species of Lepidodendron, 3 of Knorria, 4 of Halonia, 6 of Calamites, 10 to 20 species of Psaronius and other stems. This would make at least 60 species outside of the Pine family for 8 in it. The same proportion would be true according to the number of specimens. In the state of Ohio, near Athens, there is perhaps the most extensive deposit of transported silicified trunks that it is possible to find anywhere. Of some thousand specimens that I have examined, all belong to the genera Sigillaria and Psaronius. A single specimen which is not yet determined has concentric circles, and may belong to the genus Araucaria.

From recent observations, it appears that the genus Sigillaria is related to the Isoetes of our time, a water plant. All the Psaronii are trunks of ferns and like the other genera quoted above, they all belong to the flora of the true coal formations, and are found in the shales also. Nevertheless, this does not put aside that part of the assertion: that some trees of the sandstone might have been transported from a dry land. It is a complicated question which may be examined at another time.

(To be continued.)

ART. IV.-Some Remarks upon the use of the Microscope, as recently improved, in the investigation of the minute organization of Living Bodies; by H. JAMES CLARK, of Cambridge, Mass. [From the Proceedings of the American Academy of Arts and Sciences, Boston, Mass., January 26, 1859.]

I was incited to bring together my thoughts and experiences upon this subject, by discovering, three or four months ago, a novel feature in the so-called glandular dots of the wood of our common White Pine (Pinus Strobus, Linn.).

A dot of this kind is usually represented by a circle (fig. 1, C, d), in the centre of which is a single or double ring (a, b), which has about one third the diameter of the first (d). The outer circle (d) is described as the boundary of a lenticular space (A, e) between two contiguous cells, and the inner double circle (C, a, b) as the outskirts of a perforation (A, ab) in the deposit layer (ƒ)

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Fig. 1.

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of the cell. The double circle arises, as is said, from the fact that the perforation has the shape of an extremely short truncate cone, which, when viewed endwise, presents to the eye its two circular ends concentrically; the broader end, which is always next the interior of the cell, corresponding to the outer (b), and B the narrower end to the inner circle (a). Thus are these dots described and illustrated, by Mohl, Schleiden, and Schacht, as seen in the common European Pine (Pinus sylvestris), and thus did they always appear to me, not only in that species, but also when I observed them in Pinus Strobus, except with this difference, that the perforation was bounded by an exceedingly faint third circle, (C, c,) whose relations I could not comprehend, ▲ nor was I able to reconcile its presence with the theory in regard to the nature of the perforation. I therefore left it, doubtingly supposing it to be some optical illusion. The microscope which I used, and which I have been in the habit of using up to within the last six months, is an Oberhaeuser's, made for Prof. Agassiz some years ago; and yet at this very day I find it as good, with perhaps a single exception, as any now made in Germany, and therefore just as trustworthy in the investigation of the glandular dots of the Pine.*

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* It may not be uninteresting to state here, that the first great microscope made in Germany was constructed in 1829 by Fraunhofer, for Professor Agassiz. This microscope was represented in a copper-plate engraving, and described by Döllinger in the Memoirs of the Munich Academy for 1829, or 1830. In January, 1881, Agassiz went to Paris, and having given unlimited orders to Oberhaeuser for the best microscope that could be furnished, according to the knowledge of those times, he received from that maker, in 1832, an instrument which has not been surpassed in all Germany to this very day; at least, I have never seen any work from the hands of the best observers there, whether zoologists, histologists, physiologists, or botanists, which could not have been accomplished just as well by this microscope. There may be one exception to this of a very recent date, but I am acquainted with the instrument only through report. With this masterpiece of Oberhaeuser, Agassiz has gone on to this time, doing his great work with remarkable success, as all the world knows. Of late years it has become evident to Agassiz that his instrument was not equal to the demands which the progress of his researches put upon it; that there was something beyond its reach, of which he now and then could get a glimpse, just enough to warrant him in the belief that the study of the intimate structure of organized bodies had hardly begun.

So long ago as 1852 he had opportunities to see the workings of an instrument of the English pattern, made by Spencer; and although it was known as a rival of, if

For the last six months I have used one of the most recently improved microscopes, made by Mr. Charles A. Spencer of Canastota, N. Y.; and with this, between three and four months ago, I again attempted to solve the mystery of the glandular dots. This I did with the most complete success.

When the focus was brought to bear upon the inner surface of the dot, the innermost ring (B, C, a) of the perforation appeared first; a little deeper, the next outer one (b) came into view, whilst the innermost (a) disappeared; and still deeper the last (b) passed from my sight, and the faint ring (c) of my old observations came out sharply and clearly, as an exterior circle to the two others.

I also observed, when passing from the innermost circle (a) to the outermost (c), that the widening was gradual; and so, too, did it appear in the transit from the second ring () to the outermost (c). This gave me the clew to the whole structure. I saw that these rings were not the expression of a simple perforation, but of the outwardly curled edge of this aperture, shaped in such a way as to form a sort of trumpet mouth.

Although I would not trust to a transverse section alone, yet I found that it confirmed me in my views as explained above. The figures which I have given, namely, a transverse section (B) with dotted lines projected upon a face view (C) of the dot, -I think will suffice to illustrate what I believe to be the true relations of these rings,

Now, why was it that the Oberhaeuser instrument would not divulge these relations, when the microscope of Spencer succeeded so satisfactorily? This I will explain by showing the difference between the objectives of the two microscopes. I will compare the action of the objective of Oberhaeuser to the manner

not superior to the Transatlantic microscopes, he did not become convinced that it came up to his requirements.

Two or three years later I had the pleasure of bringing to his notice the results of some of my own researches upon the value of recently constructed objectives of English make. This gave him renewed hope, and, having heard of Spencer's continued rivalship and growing superiority, he determined to test his skill to the utmost. He therefore, in 1857, requested me to visit Canastota, in order to consult Spencer, and advise him as to the nature of the work for which we wished to use his instrumeuts. This consultation resulted in the conclusion that we must have three sets of objectives;-one with the extremely flat field; a second of the like kind, but so put together as to allow working with it plunged in water; and the third with a depthing focus extending as far as possible beyond that of the ordinary kind, for the purpose of viewing objects as a whole, in order to ascertain the relations of their different parts. And Spencer is now devoting those extraordinary abilities which show him to be a man of genius, to the construction of a microscope which shall embody not only the optical excellences of the different systems of lenses required for the various modes of investigation, but also those conveniences of mounting which the long use of that instrument has taught us, to facilitate the researches upon the living being in its normal condition, and in its element, that we may be no longer compelled to represent the tortured figures of a crushed body or dismembered organism.

in which a plano-convex lens treats the rays of light which pass through it, from any object. Those rays which pass near its axis are brought to a focus at the farthermost possible point from the lens, whilst the rays which pass through the periphery are converged at a much nearer point, and between the axis and periphery there are all degrees of convergence. The difference between the farthermost and nearest points of convergence may represent the distance or depth through which the objective takes cognizance of things, and will account for the fact that I saw all the rings of the Pine-dot at one time.

The action of the objective of Spencer's microscope may be compared to that of a parabolic lens, which converges all the rays of light to one absolute plane, and therefore forms what is called a flat field.

Now out of this field, either above or below its horizon, it is not possible to see anything, and on this account, when the innermost ring (B, C, a) of the dot was in view, the others were not to be observed; and when the field was lowered to the second ring (b), the innermost one (a), being above the horizon of the field, was invisible; and, again, when the outermost and lowest ring (c) was reached, the middle one (b) also vanished.

Were this outermost ring as distinct as the others, it might have been possible to detect its relations by means of the Oberhaeuser; but since it is the exceedingly delicate, reverted edge of the perforation, the narrow aperture of this ordinary objective does not admit sufficiently oblique rays to define it, to say nothing of its being confused with the other rings which are in view at the same time.

I would here remark that this peculiar structure is most frequently to be observed in old wood, when the cell-wall (B, g1) has also become perforated, and even has retreated from the deposit layer as far back as the edge of the lenticular interspace. young wood the perforation corresponds with the figures usually given. I have used this discovery, not only to show how little may be understood of the structure of a familiar and much treated of body, but also as a preliminary illustration of the exceeding value of a flat field and a wide angle of aperture in microscopic investigations.

But this is not the first example which has occurred to me. As far back as a year ago last summer I visited Mr. Spencer, and spent several days with him in testing his objectives with the tissues of every creature which we could find. I shall never forget the astonishment and delight with which I occupied day after day, plunged into the hitherto unknown depths of organic life. I say this after having tested from time to time some of the best English microscopes which have been made since the "Great Exhibition," and therefore am not to be supposed to

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