meters of gas. The cost of the oil would be therefore in Paris about a hundred times that of the electric light, or that of gas fifty times, to produce the same light. The comparison with the smaller machine would be less favorable. The carbons for the larger light had a cross section of 81 mms., and the ordinary consumption was a little over a centimeter in length per hour.Comptes Rendus, lxxxii, 299.

E. C. P.

5. Effect of increase of temperature on the Index of Refraction; by Professor T. P. MENDENHALL. Letter to the editors, dated Columbus, Ohio, April 10, 1876.-Dear Sirs: I have in progress an investigation of the effect of increase of temperature on the index of refraction, which has at this time yielded some results of considerable importance to spectroscopists. In 1858 Messrs. Gladstone and Dale announced as the conclusion of a research upon this question, that in every substance the refractive index diminishes as the temperature increases. I am satisfied that glass at least does not obey this law; that, on the contrary, with it the index increases with the temperature. In my experiments I have used equilateral glass prisms with indices of refraction of about 1.63. The change in the position of the D line has been observed with a parallel wire micrometer. That the effect was not due to a change in the angle of the prism during the process of cooling I satisfied myself-both by measurement of the angle when hot and when cold-and by receiving the image of the slit of the collimator reflected from both faces upon the cross hairs of two telescopes properly adjusted upon the instrument. No. appreciable change in angle could be discovered. Numerous experiments agree well in fixing the "index of sensitiveness," but the quantitative results I have not fully worked out. I only wish at present to direct attention to the fact, that, in the use of a train of several glass prisms in a spectroscope, ordinary changes of temperature to which the instrument may be subjected will produce a very noticeable change in the position of the spectrum lines. In my own, of five large prisms, of an angle of 64°, the change in the position of the D line on removing the prisms from an open window, the temperature outside being about 32° F., to the room, at ordinary temperature was as much as 95 divisions of the micrometer screw head. With a smaller number of prisms the change was closely proportioned to that number. I wish to suggest that in this way may be found the cause of many discrepancies which occur in tables of wave-lengths, as furnished by dif ferent workers, in such cases as those in which the dispersion spectrum has been made use of, and the wave-length computed by interpolation. A great many such cases occur in Watt's Index of spectra. In an instrument of many prisms the observation of temperature will be a matter of vital importance in fixing the exact position of a line. I propose to pursue the investigation, especially in respect to the observation of lines more or less refrangible than the D, and also as to the effect of change of temperature upon other than glass prisms.

II. GEOLOGY AND MINERALOGY.

1. Does the actual vegetation of the Globe furnish any general marks by which it could be recognized in all countries if it became fossil? This question is asked by Alph. DeCandolle in a brief article in the Archives des Sciences of Geneva for December, 1875. The question is answered in the negative, as was inevitable. For, as the author observes, the species of plants over the globe differ so widely with difference of locality that it would be exceedingly difficult, or rather, impossible, to draw the line between differences in species due to local distributions, and those due to successional relations. The difficulties, moreover, are greatly increased through the fact, well illustrated by Dr. Gray, that the vegetation of the northern hemisphere has widely changed place during even the Quaternary, and also more than once in earlier time. It hence follows, as DeCandolle urges, that any conclusions as to the succession or cotemporaneity of species in Europe could not be expected to be applicable to America or the other continents; and even the deposits of the several natural regions of a continent would not admit of being synchronized without great doubts over the conclusions. This special inference is not new to geologists; for they admit that with the best of evidence they cannot make out, except very uncertainly, the equivalency of the successive rocks of Europe and America.

But while this general proposition is well sustained, other questions are suggested by the author which appear to demand a reference to a wider range of facts than his paper considers.

Professor DeCandolle seems to regard all fossils as equally poor registers of geological age with plants. It is certain that fossil plants are a most unsatisfactory means of determining equivalency. Marine plants-in wonderful contrast with marine animals-have varied little through the geological ages; and hence if plants are used at all for chronological purposes we are confined, with hardly an exception, to the terrestrial species. But the terrestrial species, while much more diverse than the marine, include only a very limited series of distinct types, and floras have continued the same or similar through very long ages. Besides, terrestrial species, whether vegetable or animal, are more confined in their distribution through physical conditions than those of salt-water; and, further, they are far more poorly represented in the rocks than marine species. For these reasons, and because of the great doubts that come from migrations, the geologist makes little use of fossil plants except for the purpose of characterizing in a general way the floras of the grander divisions of geological time. In actual fact, geologists, in their subdivisions or identifications of formations, have relied almost solely on evidence from fossil animals, and especially marine animals; and if fossil plants are mentioned as the characteristics of a period or age, it has been, with rare exceptions, only after the question of the period or age has been decided by means

of other evidence. Evidence from these other sources has its doubts, but it is not of so small value as that from plants. This comparative want of value is well illustrated by the present wide divergence between Paleophytologists and general Paleontologists with regard to the age of the plant-bearing beds of the Rocky Mountains, the Arctic regions, and Europe. An allusion to the uncertainties of Botanical evidence in the Rocky Mountain region may be found on page 149 of this volume.

But Prof. DeCandolle makes the evidence from plants of less value, we think, than is reasonable. He says: No one would dare to assert that during the progress of a given bed of Pennsylvania coal, there did not exist somewhere, perhaps far away, an elevated region less moist, on which Angiosperms were already in existence. The supposition is a forced one. For, in Cretaceous and Tertiary times, Angiosperms were the plants of moist lands, their leaves abounding in the coal-formations of those eras; and it is hence natural that they should have abounded in moist places also in the Carboniferous age, if in existence then along with the Acrogens and Gymnosperms.

In the Carboniferous period of North America, the peat-making marshes at times spread from Eastern Pennsylvania to Western Iowa and Arkansas, covering an area of more than 500,000 square miles; and, at the same time, there were dry hills or mountains along the borders of the marshes, in New York, New Jersey, Ohio, Wisconsin, Missouri, Arkansas, through all that long age. The Adirondacks were certainly in existence, and the Green Mountains, and the Highlands of New Jersey, and other ridges or mountains beyond the Mississippi. The area of those Carboniferous marshes with their surroundings was large enough, and varied enough in surface, to have borne a fair representation of the flora of that era of approximately uniform climate; and still the streams from the hills conveyed, so far as yet discovered, no leaves of Angiosperms to the marshes that bordered the hills. The Coal-measures of the Arctic bear similar testimony, whether there by migration or not, and so do those of Europe. Further, Permian, Triassic and Jurassic beds overlie the Coal formation both in America and Europe and have afforded no remains of Angiosperms. It is from facts like these that geologists have been led to infer that the flora of those lands during the Carboniferous age had characteristics distinguishing it very decidedly from that of other ages; and to deem it probable that the precursors of the Angiosperms existed then in a state unlike that of a Cretaceous or modern Angiosperm.

Prof. DeCandolle adds, in the same paragraph, that if fossil Angiospermous plants were found by geologists in any rock "that rock would be at once pronounced of the Cretaceous age," [or of later time]. In reply I only repeat that geologists are very generally convinced that the evidence from fossil plants is not to be trusted, and make the plants of whatever age the fossil animals present may indicate. The "Cretaceous" plants of the United States are

the plants of beds which had previously been determined, through the animal fossils, to be Cretaceous; and, if geologists finally conclude that the flora of the Lignitic beds is all Cretaceous, it will be done on the ground of the animal relics, and in spite of what has been regarded as good botanical evidence.

While then there may be doubts over chronological conclusions from fossils of whatever kind, the geologist who surveys the whole field finds those doubts less weighty than they would naturally appear to one who looked at the subject from the botanical side alone.

J. D. D.

2. Report of the Geological Survey of Ohio. Volume II. Geology and Paleontology.-Part. II, Paleontology, (or, as stated on the cover, Paleontology, Vol. II.) 436 pp. roy. 8vo, with over sixty plates. Columbus, Ohio, 1875.-This large volume contains, after a preface, by Dr. J. S. Newberry, the head of the survey, descriptions of Fossil Fishes, by DR. NEWBERRY, pp. 1-64; of Silurian Fossils, and of Crinoids from the Waverly group, by J. HALL and R. P. WHITFIELD, pp. 65-179; of Silurian and Devonian Corals, by H. A. NICHOLSON, pp. 181-268; of Invertebrate Carboniferous Fossils, by F. B. MEEK, pp. 269-347; of Carboniferous Amphibians, by É. D. COPE, pp. 349-411; of Lower Car boniferous fossil plants, by E. B. ANDREWS, pp. 413-426. The paleontological work was thus in able hands, and covers a large number of species in each of its departments. The portions giving the most novel results are those of the Fishes and Amphibians, and the Lower Carboniferous plants.

Dr. Newberry describes the genus Dinichthys from new and magnificent specimens including broad plates of the venter and back, fifteen inches to two feet in length, a mandible twenty-two inches long, a cranium almost complete, and other bones-and shows that it was closely related to Coccosteus. The large ventral pieces were five in number. The anterior end of the mandible was turned up so as to form a strong acute prominent tooth, which had a produced dentate margin in one species. The dentition resembles that of the living Lepidosiren; and Dr. Newberry refers the genus (along with Coccosteus, Heterostius, Asterolepis, Pterichthys, etc.), to the Lepidosiren group, or the Dipnoa, and agrees with Dr. Günther in placing the Dipnoans and Placoderms with the Ganoids. A species of Coccosteus, C. occidentalis Newb., is described from Ohio. Dr. Newberry describes "Conodonts" from the Waverly group, which he is inclined to refer to the Marsipobranchs. He also gives new species of Cladodus, Polyrhizodus, Orodus, Ctenacanthus, Lystracanthus, Platyodus, Rhynchodus, Ctenodus, Dipterus, and introduces the new genus of Ganoids, Heliodus, for species near those of Dipterus. Dr. Newberry, after remarking that the occurrence together of the spines Ctenacanthus furcicarinatus, the teeth Orodus variabilis, and certain dermal tubercles, show that they belong to the same species, remarks that impressions of the heterocercal tail, with the fins of the same species, have been observed-one of them six

feet long; and that the lower lobe of the tail consists of rays that were distinctly ossified.

The Batrachians or Amphibians from the Carboniferous beds, and described by Prof. Cope, are referred by him to the order which he has named Stegocephali; an order including the Labyrinthodonts Owen, and also Owen's Ganocephala, and other species recently described which have been called Microsaurs. The species are partly lizard-like, with ribs and limbs (as in Dendrerpeton, Hylonomus, Amphibamus, Colosteus, Archegosaurus, etc.; and part very long and slender, snake-like, with limbs wanting, as in Molgophis Cope, which has ribs and probably no limbs, and Phlegethontia Cope, which is without both, and includes " batrachian snakes,"-one imperfect specimen having 56 vertebræ. Prof. Cope also describes a few Amphibians which he refers to the Proteida.

true

The interesting Subcarboniferous plants brought to light and described by Professor E. B. Andrews, have been already noticed in the last volume of this Journal (p. 462) by the author. The turning out of so many new species of unusual forms in a region that had already been long explored is a fact of much geological interest.

The very numerous plates of this volume are well executed.

Dr. Newberry announces in his Preface that Volume III of the Paleontology will contain a general review of the fossil plants of Ohio, with descriptions of new species; a memoir by Prof. O. C. Marsh, on the Dicotyles compressus, and on the Castoroides Ohioensis; and notices of other Quarternary vertebrate remains, together with some invertebrate fossils yet undescribed. When completed, the series of Ohio reports will rank among the best State-survey publications that have appeared.

3. Geological Survey of Alabama. Report of Progress for 1875; by EUGENE A. Smith, Ph.D., State Geologist. 8vo, 220 pp. In this volume, a general outline of the Paleozoic formations of Alabama, with brief descriptions of the various beds, by Prof. Smith, is followed by a summary of the facts heretofore known concerning the Coal-fields of the State, prepared by Mr. T. H. Aldrich. The first systematic attempt at mining and shipping coal, in Alabama, is said to have been made in 1853, near the southwestern extremity of the Cahaba coal-field. Mr. Aldrich's paper includes a reprint of parts of an elaborate essay by R. P. Rothwell, published, two years since, in the Engineering and Mining Journal. The coal-series is said to contain ten or twelve veins [seams] of remarkable thickness, i. e., from two feet (average thickness of clean coal) upward, besides a number of smaller beds, several of which are from fifteen to eighteen inches in thickness. These ten or twelve workable beds are distributed in two series or groups, as we find in all our coal-fields, notably in West Virginia, Ohio and Pennsylvania. The maximum available thickness of coal as yet proved in any portion of the field will not exceed thirty or thirty-five feet; while, if we take the area of the

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