topped Chimborazo, and that after a violent eruption, which lasted eight years, the walls fell in. The plain of Riobamba is covered with fragments of trachyte, the debris of the last cone.

Twenty-five miles S. E. of Riobamba, is the ever active Sangai. Little is known of this busy volcano, as the marshes surrounding it and the great depth of fine ashes on the sides, render it unapproachable. It is constantly ejecting ashes and incandescent stones (LaCondamine adds "sulphur and bitumen,") accompanied by hourly explosions sometimes heard at Guayaquil. It is said to be more active in winter than in

summer.

3

From these examples it will be seen that the products of the Ecuadorian volcanoes are mainly feldspathic. Trachyte abounds throughout the Andes. All the summits which rise above the limit of perpetual snow are trachytic. The trachytes of Bolivia, says D'Orbigny, are always micaceous; those of the equator are cellular, porous, granitoid, granular or compact. Cotopaxi alone produces foam-like pumice.* A most perfectly glassy translucent obsidian is occasionally found on Cotopaxi and Chimborazo. Its sp. gr. is 2.35 to 2:40. Humboldt mentions pitchstone as occurring on Antisana. There are numerous rocks on that volcano, and especially on Tunguragua, which exhibit a black vitreous base resembling pitchstone, but it is anhydrous, (losing only of its weight by ignition,) and is therefore a soft trachytic glass. A coarse variety, approaching "ribboned obsidian," we found on Antisana. Some of the porphyritic rocks are conglomerate; but the great majority are true porphyries having a homogeneous base. Dr. Hunt calls them "porphyroid trachytes." Many of the specimens would be labeled Andesite by Darwin; but we demand a uniform and more definite definition of the term before using it. They have a black, rarely reddish, vitreous or impalpable base approaching obsidian, with a sp. gr. of 2·59 in pure specimens, and holding crystals of glassy feldspar and sometimes of pyroxene and hematite. They differ from the Old World porphyries in containing no quartz and seldom mica. The absence of basalt as well as the paucity of quartz is noticeable. Granitic rocks, also, so abundant in eastern South America, are rarely visible on the Pacific side, in the neighborhood of volcanoes. But they are only covered by

*James S. Wilson, C. E., in the employ of Ecuador, claims the discovery that pumice is not a rock produced by volcanic fusion, but simply a rock altered by the solution and removal of one or more of its ingredients by humid heat, probably assisted by gases and acids. Thus the pumice of Pichincha is granitic, and specimens are found showing gradations of change from compact stone to porous pumice." It is remarkable that true trachyte, pumice and obsidian are wanting in the Galapagos only 700 miles from Pichincha. According to Pentland, trachytic pechsteins, obsidians and other vitrified products are very rare in Peru and Chili.

volcanic accumulations. At Cuenca, south of Chimborazo, metamorphic rocks abound. On the east slope of the eastern Cordillera mica-slate is the prevailing rock. The "prodigious beds of gypsum" seen in Chili are wanting in Ecuador. A dolomitic marble occurs near Cayambi.

The valley of Quito is doubtless filled up, like the Bolivian plateaus, with the debris of granitic and ancient sedimentary rocks, but it is now covered by a vast layer of pumice and scoriæ which have been falling from the early tertiary to the present time. Nearly the only fossils brought to light are some pleistocene mammals. At Alangasí, six miles from Quito, teeth of the Mastodon (Andium ?) have been found; and in the ravine of Chalan seven miles south of Riobamba, we discovered the femur and patella of a Mastodon, the skull of a Horse, and numerous leg-bones not yet identified. They were imbedded in the middle of a cliff (200 ft. high) of the compact tenacious clay resulting from the union of trachytic ashes with water, and were associated with terrestrial shells, identical with living species in the vicinity. The bones were drifted to this spot and deposited (many of them in a broken state) in horizontal lines. It is interesting to speculate upon the probable climate and the character of the vegetation in this high valley, when these extinct mammifers lived.*

Rochester, N. Y., Nov. 10th, 1868.

ART. XXI.-Observations upon Autumnal Foliage; by JOSEPH WHARTON.

If chlorophyl, the green coloring matter of leaves, should be, like many other greens, a compound color, it must have for one of its elements a vegetable blue, capable of being reddened by acids.

If the juices of leaves, kept in a neutral condition by the vital force, or by alkaline matter brought in the sap from the earth, should, when circulation ceases, become acidified by the atmospheric oxygen, those juices would then be capable of reddening the vegetable blue of the chlorophyl

If, however, that vegetable blue should be thus reddened, it ought to become blue again, when exposed to an alkali; or, in other words, if green leaves should be reddened in the autumn in the manner here suggested, by the unresisted action of the oxydizing atmosphere, they ought to return from red to green, if immersed in an alkaline atmosphere.

* See further, on this subject, an article on the heights of the South American Andes of Ecuador, etc., by Dr. Moritz Wagner, in the Berlin Zeitschrift für Allgemeine Erdkunde, xvi, 232, 1864.

Reasoning thus one autumn day about ten years ago, I arranged a wire staging, to stand under a glass receiver, which dipped into a dish of water, and under which was also placed a capsule containing ammonia. Upon this staging I placed in succession a variety of autumnal red leaves, and had the gratification to perceive that in most cases the green color was restored.

The rapidity and completeness of this restoration varied greatly in different leaves; while those which were covered by a thin and porous cuticle passed visibly from red to green before the eyes, (for instance Sassafras, Blackberry, Maple, etc.), others, whose cuticles were comparable to an impervious varnish, (for instance some of the Oaks,) changed gradually into brown, without showing any trace of green, except sometimes in a few spots where an imperfection in the leaf existed.

In order to determine fully whether the behavior of this latter class of leaves was really owing to the protection afforded to the pulp or chlorophyl by the cuticle, I wounded several such oak leaves in divers spots, and found that although these leaves, when exposed to ammoniacal vapor, became generally brown, each wound became the center of an irregular patch of green.

Of course the final result of exposure of any leaf to the vapor of ammonia, is destruction of all delicacy of tint, and production of a general decaying brown color; but the restoration of green is perfectly distinct, and this green color endures for some minutes, or even hours, if the leaves are soon enough removed from the vapor.

This simple experiment had more significance for me, when I read, a few years afterward, that the distinguished French chemist Frémy, had actually separated chlorophyl into two distinct substances, one blue, the other yellow.

Frost probably plays no other part in causing the autumnal tints, than merely to arrest the circulation by killing the leaves. When a sharp frost occurs early in the Fall, while the pulp of the leaves is still full and plump, the red colors come out brilliantly, because there is plenty of the blue substance to be acted upon by the juices, then also abundant.

When on the other hand the leaves die slowly and are at the same time slowly dessicated in a late and dry autumn, the pulp becomes so meager, and the skin so dry and hard, that an abundant production of fine red tints is impossible, and brown, the color of decay, predominates.

The connection between arrest or feebleness of circulation and reddened foliage, is well illustrated by the Sassafras, the leaves upon the extremities of whose branches are usually well

nourished and succulent, while the inner leaves-those nearer the trunk-are smaller and weaker. It is not uncommon for a Sassafras tree, which stands alone, to present in the autumn the appearance of a green mass of foliage, illuminated from within by red and yellow lights: this results from the complete change of those feeble leaves in the interior, before the more vigorous outward leaves are in a condition to yield.

An Oak tree, observed last Fall, afforded a similar illustration. Twigs had sprouted from the trunk, and the leaves upon those twigs all reddened long in advance of the leaves upon other parts of the tree. When, shortly after, and long before the general stripping of the tree, those twigs fell, they appeared upon examination to have been detached from the trunk thus early by a process similar to that which separates the single leaf from the plant, and whose first effect had of course been an untimely stoppage of the circulation.*

Leaves which die in the Summer are usually dried out directly, or, if the weather is moist, are quickly rotted; still, it is common enough to see single dead leaves of Gum, Sumac, or Sassafras, splendidly reddened many weeks before a frost.

In June, 1868, I observed leaves of Mahonia upon a sickly twig thus colored, and on July 19th, I found thoroughly reddened leaves of Sassafras and Gum, and leaves of American Poplar and Chestnut of perfect autumnal yellow; all being of course such as by feebleness of, or injury to, the sustaining twigs, had been deprived of their circulation.

It is somewhat remarkable, however, that of the millions of dead leaves which I saw last Summer upon twigs wounded by the seventeen year locusts, not one showed autumnal tints; though I observed upon a number of trees, bearing the brown leaves of the locust-wounded twigs, an occasional leaf of a full autumnal red upon a twig not so wounded.

For the convenience of those who may incline to pursue this subject, I add a compend of some of the principal recent investigations concerning chlorophyl and related matters.

Comptes Rendus, 1, 405. Frémy separates chlorophyl, when

*The Medical Press and Circular, of Paris, states that M. Trecul and others have lately been engaged in investigating the cause of the autumnal stripping of trees, and their researches would seem to point to the conclusion that in many plants a phenomenon occurs just before the fall of the leaf, which is not unlike the process which accompanies the shedding of horns in animals. It consists in the obstruction of the proper vessels at the base of the petiole, or leaf stalk The obstruction. according to an American writer, is caused by the multiplication of cells, which first occurs in the parietes of the vessels. The cells increase and multiply, till at last the vessels are completely choked up in the neighborhood of the insertion of the leaf, and thus a differential plane is formed, across which the leaf stalk breaks, and the leaf accordingly falls.

dissolved in alcohol, into two coloring matters, by submitting it to a mixture of ether and chlorhydric acid; the former takes up the yellow matter, (phylloxanthin,) the latter the blue matter (phyllocyanin,) each liquid having distinctly the yellow and the blue color respectively, which being mixed by shaking together, form a leaf green. The yellow coloring matter of new sprouts, and of etiolated leaves, contains phylloxanthin, capable of being developed into chlorophyl; in autumnal yellow leaves, the phyllocyanin has been destroyed. The yellow matter, Frémy supposes to be more universal and more stable than the blue.

Comptes Rendus, lvii, 39. Châtin and Filhol state that the surface of young leaves is covered with a fatty substance, protecting the tissues from the air, which varnish diminishes toward Fall. This being removed, the leaf becomes dead colored. Deoxydizers (e. g., SO) restore red leaves to yellow. Red leaves contain yellow matter deeper in, below the red. Leaves remaining yellow, are so because the oxydation which turns green leaves first yellow and then red, has been arrested in them at the yellow stage. (This appears to me by no means applicable to such yellowed leaves as the American Hickory and tulip Poplar.-J. W.)

Comptes Rendus, lxi, 188. Frémy reports that he obtains pure chlorophyl as follows. By agitating hydrate of alumina with the ordinary alcoholic solution of chlorophyl, a green paste or lac is obtained, a fatty substance which accompanies chlorophyl being left in the alcohol. This green paste being afterward boiled in alcohol, the latter takes up from the alumina pure chlorophyl, which is deposited when the alcohol is afterward sufficiently diluted with water. Chlorophyl thus purified, being boiled long enough with hydrate of baryta, is decomposed into phylloxanthin, (a neutral body, analogous to glycerin,) and phyllocyanate of baryta. The mass of precipitate containing these two substances, being treated with alcohol, the phylloxanthin is dissolved, and is obtained by evaporation in crystals, yellow plates, or reddish prisms. Phyllocyanate of baryta, treated with SO3, yields its acid, which is insoluble in water, but forms an olive colored solution in alcohol or ether; dissolved in SO3, or HCl, it gives liquids, which according to their concentration are green, reddish, violet or beautiful blue. Frémy does not consider chlorophyl a simple mixture of its constituent substances.

Comptes Rendus, lxi, 371. M. E. Filhol shows that the treatment of chlorophyl by acids decomposes it, and produces substances not preexisting. No substance, therefore, got from