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As to the result I maj' say that I have not yet met an immersion lens by any first class American, English, or Continental maker of an actual focal length of J inch or less which did not. in my hands, resolve the Amphipleura more or less satisfactorily. I have even succeeded with an immersion £ of Mr. Tolles' obtaining a good photographic negative of two frustiiles well resolved with only two hundred and fifty-six diameters. My friend, Dr. J. W. 8. Arnold of New York, writes me that he has obtained resolution by a Wales's immersion J.

A great difference exists, however, as to the manner in which different objectives, even when of the same power and by the same maker, will exhibit them, and for myself I have obtained the best results only with the finest immersion glasses of Messrs. Wales, Tolles, and Powell and Lealand. Spencer's recent objectives I have had as yet no opportunity of trying. With dry objectives the task is more difficult, still I have succeeded tolerably with some of the dry objectives of the above makers, and it was as seen with dry objectives that Messrs. Sollitt and Harrison first observed the stria?, though they could have glimpsed them but imperfectly or they would not have set them down at one hundred and thirty thousand to the inch.

In illustration of the appearances which ought to be obtained by a first class immersion objective of adequate power, the liberality of the Editors of the Natukalist enables me to present herewith a Woodbury print from a negative, representing portions of two Amphipleura frustules as seen by an immersion objective of Mr. Win. Wales of Fort Lee, New Jersey, magnified about fifteen hundred diameters. The lower of the two frustules proved on a careful count in the microscope, to have ninety-five striae to the roW °f an inch. This circumstance puts it in the power of every one to compare the two frustules, and to determine the precise magnifying power of the print.

The objective used was made by Mr. Wales nearty three years ago. It was named a Jff but is in fact a lower power. On measurement I obtained the following data. Magnifying power, without eyepiece, at fifty inches distance from micrometer to screen eight hundred and ninety diameters uncovered, twelve hundred ami fifty diameters at full correction for cover; angle of aperture at uncovered 110°, at full cover 130°; at uncovered the objective is, therefore, -fa very nearly.

The photograph was taken without an eyepiece, the magnifying power being obtained by distance: owing to the moderate angle of the objective the picture was freer from diffraction fringes and consequently handsomer than any Amphipletira picture I had previously obtained, for this reason only it was selected for reproduction. Since it has been in the hands of the printer, however, it is only fair to say that I have obtained equally beautiful pictures with the same power by an objective made by Tolles of 140° angle, as well as by an objective of Powell and Lcaland, both used without eyepieces. Copies of these pictures I have sent to the Editor of the department of microscopy of this journal for exhibition. I suspect each maker would claim that the picture by his objective was the best. For myself I regard them as nearly equally good, and think that to discriminate slight shades of excellence between objectives of this high grade, it is necessary either to give a much higher power, by distance or eyepiece, or else to use some more subtile test, such for example as the finer bands of the Robert's plate.

My present object is not to advocate one maker or another, but to present an image of what the best glasses of several excellent makers will do with ease if properly handled, and to those who are influenced by more partisan feelings I need only suggest that less than two years ago no American microscopist had been able to see any striaj on this well marked diatom, and that those who had made the attempt were disposed to regard the observations of the Hull naturalists, made over ten years before, as quite fictitious.

In conclusion I need only mention that the illustrative print was reproduced from my negative by "The American Photorelief Printing Company "No. 1002 Arch Steet, Philadelphia, Pa.

WHAT IS TRUE TACONIC?

BY PROP. JAMES I». DANA.

The true use of the term Taconic should lie learned from Prof. Emmons's first application of it when he made his formal announcement of the "Taconic system." In his final New York Geological Report, 4to., 1842, the rocks so-called are those of the Taconic mountains, on the borders of Massachusetts and New York, together with the quartzite, limestone, and slates adjoining on the east,* and not the slates far west of these mountains; f moreover the slates, the rocks of the mountain, were the typical beds, and not the quartzite. Hence, if there are any Taconic schists or slates, those of the Taconic range are the rocks entitled to bear the name, being Taconic geographically, and Taconic by the earliest authoritative use, Prof. Emmons the authority.

Prof. Emmons, in his Agricultural Report, subsequently published (in 1843), announced the Primordial beds of Bald Mt. (near Canaan Four Corners, in Columbia Co. N. Y.), as Taconic also; but this did not make them so. lie referred to the Taconic the Black slates of northern Vermont, since shown to contain primordial fossils; he searched the country north and south for other Taconic rocks, and found them as he thought; and he set others on the search, not only in this country, but over the world. But all this has not changed the fact that the true Taconic beds, if any are such, are those he first so announced; and that the rest, so far as they are of different age from these, younger or older, have been dragged into the association without reason. The Taconic rocks of Berkshire and of the counties of New York just west always bore the most prominent part in his later descriptions of the Taconic system.

The error on the part of Prof. Emmons, in referring beds of other ages to the Taconic system, is not surprising considering the difficulties in the case. But it was no less an error; and his name as a backer cannot make the wrong right.

♦Professor Emmons opens the subject of the "Taconic* System " in his final Report (1842) by saying that it extends north through Vermont to Quebec, and south into Connecticut; but the only rocks he describes as the rocks of the system arc those of Berkshire County, Massachusetts, and their continuation westward into New York. These are the typical rocks on which the system was founded. On plate xi. four figures representing sections across this particular region are given. The only Vermont observations are contained in the only other section on the same plate representing a section from Lake Chan-plain to Richmond, Vt.. through Charlotte. No description of the rocks of this section is to be found in the text of the volume.

t In figure 4 of plate xi (referred to in the preceding note) representing a. section through (iraylock, the '• Taconic slate" stops just west of Iterlin. Rensselaer County. New York, the slates on the west being put down as " Hudson River shales.'* and in figs. 2 and 3, the boundary is near Petersburg, north of Berlin. The extension of the Taconic to the Hudson River appears first in Prof. Emmons's Agricultural Report, published in 181.'!.

Geologists now regard the slates of Tacouic Mt. and the limestone, also, as of Lower Silurian age, but later than the Potsdam sandstone. Logan refers them to the Quebec group. Whatever the period of the slates, or slates and associated limestones, to that period properly pertains the term Taconic.

THE STONE AGE IX NEW JERSEY.

[Concluded from March Number, p. 160.]
BY CHARLES G. ABBOTT, M.D.

Arrowheads.— No one class of relics of a savage race presents at once so great a variety of shapes, sizes and materials; and the former presence of "Indians,"is more generally known to the people at large through the frequent occurrence of these arrowpoints, than by means of any other style of weapon or implement; not even excepting the cumbrous axes that not unfrequcntly go to make 11(1 the piles of cobblestones that accumulate in field corners or by the roadside. One of the largest axes we have seen, which we have since sent to Sir John Lubbock, was found supporting a section of worm-fence, where it had been lying thus for at least a century.

These arrowheads, which are found scattered over every portion of the state, are, very naturally, much more numerous in some localities than in others; and as no one style appears to be peculiar to any one locality, a good series from even a very limited extent of country will usually represent the shapes and sizes found over the whole state. Any attempt at classification will prove a desperate undertaking, as no well marked style has yet been found which has not been duplicated by a second, varying a mere trace, and these slight variations go on without a break until the two extremes of shape are found to be connected by an unbroken chain of closely allied varieties. The Darwinism of arrowheads needs no supplemental theory to make it good, nor are there shapes that cannot be explained by a somewhat similar and more primitive one. Prof. Nilsson ("Stone Age in Scandinavia," Eng. eel., page 43) says " we may divide arrowheads into such as have,

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and such as have not, a tang or projection for insertion into the shaft." Referring to Lubbock, in "Prehistoric Times," we find him, on page 98, quoting Sir AV. R. Wilde, who divides the arrowheads into five varieties. Further reference to the two works quoted above shows us, in the drawings, that whatever they have illustrated from the north of Europe or from Terra del Fuego is also to be met with here in New Jersey. We propose, in figuring the various shapes that we have so far met with, to follow Prof. Nilsson in separating the specimens into those with and without tangs or projections; but we cannot undertake to follow him farther, where he specializes certain forms as harpoonpoints, etc., etc. That some were used as spears, as weapons in battle, and others as hunting spears, or for fishing, i. e., harpoonpoints, is probably beyond question; but that they were not or could not have been used as arrowpoints is difficult to disprove; and while we propose to speak of certain specimens in order, as to their probable use, we will call them all "arrowheads." Ethnologists can reject

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the text if they see fit, but we trust the illustrations will be interesting to those who desire to study them carefully, and with whom specimens arc scarce. Arrowheads with tangs or projections for insertion into the shaft are somewhat less abundant than those without the projection; but they are of far greater variety of outline, and vary more in their size, running into spear or harpoon

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