is best shown by the second figure in the lower row.* The color of this mica by transmitted light, is a pale green, and the mineral seems to agree in external characters with the substance from other localities. Considerable quantity of it was found loose in the vein, mixed with broken crystals of rutile. The only appearances at all analogous to those just described, which had come to the knowledge of Mr. Alger, were those mentioned and figured by Dr. McCulloch, and described in Vol. II. of the Geological Transactions of London. But in this case, the substance was chalcedony, and the imbedded masses composed of chlorite, had nothing of a crystalline structure, and in fact were rather imitative of vegetable, arborescent forms.

STRIATED QUARTZ CRYSTALS.

THE above figure represents some of the stria which appear on the acuminating planes of the crystals, and are parallel with their edges of combination with the adjoining planes, as shown in the figure on the next page. They are usually mere superficial triangular lines so slightly impressed as to be visible only when held in a particular position in regard to the light; but in a few cases, these configurations, commencing at a small point before the crystal had attained its full size, continue to widen with every fresh layer of particles deposited upon the faces of the crystal, until they produce cavities of considerable depth. That they were formed in this manner, is indicated by the step-like appearance of the sides of these cavities - an appearance which is more strikingly presented in a few cavities of a different * Prof. Hubbard's specimen presented the appearance in so marked a manner, as to lead to the impression they were rutile.

† A portion of this carefully separated, was found to lose nearly 15 per cent. of water when heated to the melting point of glass. A peculiar empyreumatic odor was at the same time given out, but there was no reaction of fluorine. Exposed in a platinum crucible to a white heat for twenty minutes, it became grayish black and partially fused into a mass. In this state it was slightly magnetic. The large proportion of water seems to ally it with ripidolite, or perhaps with hydro-mica from the Alps-Wasserglimmer of M. Morin. It will be further investigated.

shape, of one of which the following figure furnishes an example. In this, it will be noticed, the cavity is rhomboidal, and might at

first be mistaken for the impression left by some foreign substance which had disappeared. No substance having such form, has been found attached to any of the crystals from this place, and although the angles at which the sides meet each other, (about 76° and 104°) are nearly those of calcspar, or carbonate of iron, it is evident from the enlargement of the cavity towards the surface of the crystal, or the hopper-like appearance assumed by it, that neither of these substances could have produced it. The quartz, while depositing itself around either of them, would have taken the exact form of either, precisely as we see such impress of their forms in other crystals of subsequent formation. So it is evident, that if any substance ever occupied the cavity, it must have received its form from the cavity, without communicating any to it; and thus a pseudomorphous crystal may have been produced in a manner somewhat different from usual. It is not easy to trace any relation between these last named cavities and the crystalline structure of the quartz; their sides are not parallel with any of the striæ as seen upon the faces of the crystals; they indicate an interruption in the process of crystallization, by some cause not easily explained. The cavity measures one inch on a side, and is one half

inch in depth. It is exactly represented by the two small figures below, drawn in full size from a cast of it. The crystal itself, rhombifere of Haüy, has the replacement of rhomboidal planes on the adjacent lateral

angles of the prism, and not, as is usually the case, on the alternate angles. It is permeated in every part by acicular rutile. It is possible that a comparison of other specimens, should any more be found, will result in showing an agreement between the sides of these cavities and the edges of the small rhombic replacements lettered s. In this crystal, owing perhaps to some distortion, there is not so close an approximation to parallelism between the edges of the cavity and of these replacements, as would otherwise have obtained. No such cavity as this had been described before, and if the view here taken of it be correct, we have only to suppose a successive retrocession or withdrawal of particles in such parallel directions, thus enlarging the cavity outwardly, as the crystal itself increased in size. Something of the same kind is observed in artificial saline crystals. Several smaller cavities of the same form are presented by other crystals from the same locality, in some of which, delicate needles of rutile pass through the cavity unbroken deeply penetrating the quartz.

their extremities

ON THE APPLICATION OF THE PRINCIPLES OF ACOUSTICS TO THE CONSTRUCTION OF LECTURE-ROOMS, &C. BY PROF. HENRY.

[Not received.]

This communication was followed by remarks from President EVERETT and President SPARKS.

ON THE DIFFERENCES BETWEEN PROGRESSIVE, EMBRYONIC, AND PROPHETIC TYPES IN THE SUCCESSION OF ORGANIZED BEINGS THROUGH THE WHOLE RANGE OF GEOLOGICAL TIMES.

It was a great improvement in our zoological investigations when the differences in their relations, according to the various degrees of

affinity or analogy, which exist between animals were pointed out, and successively better understood. In earlier times, zoologists made no distinction between the different relations which existed among animals. Affinity and analogy, so dissimilar in their essential char. acters, were constantly mistaken one for the other; and upon the peculiarities which struck the observer most at first sight, animals were brought together, sometimes upon the ground of true affinity; sometimes also, upon the ground of close analogy. And, though com. parative anatomy did put the mistakes arising from such confusion right, by showing that external appearances were sometimes decep. tive, and that a more intimate knowledge of internal structure was necessary fully to understand the real relations between animals, there remained, nevertheless, a degree of uncertainty in many cases, as long as the principles of affinities and of analogies were not fully distinguished. Every naturalist now knows that true relationshipaffinity, depends upon a unity in structure, however diversified the forms may be, under which their fundamental structure is displayed. For instance, the affinity of whales and the other mammalia, was not understood, before it was shown that, under the form of fishes, these animals had truly the same structure as the highest Vertebrata.

Again, the forms of Cetacea exemplify the analogy there is between whales and fishes. They are related to mammalia; they are analogous to fishes. They bear close affinity to the mammals which nurse their young with milk; they have rather close analogy to the gill-breathing fishes.

Since the fossil animals which have existed during former periods, upon the surface of our globe, and which have successively peopled the ocean and the dry land, have been more carefully studied than they were at the beginning of these investigations; since they are no longer considered as mere curiosities, but as the earlier representatives of an order of things which has been gradually and successively developed throughout the history of our globe, facts have been brought to light, which now require a very careful examination, and will lead to a more complete understanding of the various relations which exist between these extinct types, and those which still continue to live in our days. Upon close comparison of these facts, I have been led to distinguish two sorts of relations between the extinct animals, and those of our days, which seem to me to have been either overlooked or not sufficiently distinguished. Indeed, the general results derived