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In regard to the organic character of these strata, the opinion expressed in my first paper has, on the whole, been confirmed by later researches, and is at present supported by a much greater number of facts. Most of the fossils belong to known types of the cretaceous formation. The number of species, however, exactly identical with described species is very limited. By comparing the fossils with those of the different divisions of the cretaceous formation as they are established in Europe, it appears that the rocks of Texas do not agree in any particular with received divisions. It is evident only that they belong to the upper part of the cretaceous formation, for there is a complete absence of all the characteristic forms of the gault and lower greensand, and on the other hand, there is an undoubted analogy with the organic character of the chalk and chalk marl.
Notwithstanding the considerable thickness of the whole system of strata, (which cannot be less than about eight hundred feet,) it seems impossible to divide it into different groups. Neither the mineralogical constitution of the rocks, nor the distribution of the organic remains allows of any such division. By a comparison of these cretaceous deposits with those of New Jersey, and other localities on the Atlantic coast, the difference in the zoological character appears hardly less striking than the difference in the mineralogical constitution which was alluded to before. Except the Pecten quadricostatus and the Erogyra costatu, (the latter being rare in Texas,) I do not know of any other identical species, and the number of closely allied species is not very small. A little more analogy seems to exist with the cretaceous deposits of Alabama and Western Tennessee. At least a species of Ammonite, common at Prairie Bluff in Alabama, occurs also in Western Texas, and a species of Hippurite is closely allied to a species which I found at Austin, Texas, if not identical with it.
The analogy of the Texian strata with the cretaceous deposits on the Upper Missouri, is hardly greater than with those on the Atlantic coast. Not one of those beautiful species of Scaphite, Baculite and Ammonite, discovered by Nicollet, and described by Morton,* has been met with in Texas.
The entire absence of the Belemnites mucronatus, and every other Belemnite, is one of the principal negative characters of the Texian strata.
It is more difficult to define in a few words, the positive character of the Fauna.
All the species except a very few, (which form perhaps two new genera,) belong to genera which are either peculiar to, (as for instance, Baculites, Turrilites, etc.,) or are represented in the cretaceous formation.
*Journal of the Acad. of Nat. Sc. Philad., vol. viii., p. 2.
Among the latter, the genus Exogyra, acts a very important part in the constitution of the fauna, some species of the genus having a very wide geographical range, and occurring almost everywhere in a great number of individuals. One species which resembles a Chama in external shape, composes at some localities, whole beds of itself, and is met with through the whole extent of the hilly parts of Texas.
Another still more important fact must be considered in the general distribution throughout the whole formation of the genera Hippurites and Caprina. The former being entirely wanting in the cretaceous deposits of New Jersey, makes its first appearance towards the south, in the cretaceous strata of Alabama, where it is represented by one single species, of which only a few specimens have been hitherto discovered.* In Texas, at least three species of the same genus have been recognized, and those are of wide and frequent occurrence. The genus Caprina which has never been met with, either in New Jersey, or in Alabama, is one of the most characteristic and abundant types in the siliceous limestone of Texas. One species in some places constitutes of itself whole strata. It is well known that these two genera act an equally important part in the cretaceous strata in the Alps and around the Mediterranean, whereas they are hardly represented at all in the cretaceous formation of England and Germany. An interesting analogy is hereby established between the Texian deposits of the cretaceous period, and those of the south of Europe, the more striking, if we consider at the same time, the similarity of mineralogical constitution. Between the continents of America and Europe, there must therefore have existed at the time of the cretaceous period, such a relation that in both, the same modifications in the zoological character distinguished the marine Fauna of the norih from that of the south. And thence, we proceed farther to the interesting conclusion, that the same southern inflection of the isothermal lines which is at present so remarkable in their course from the west side of the continent of Europe towards the east side of the continent of America, already existed at a period of the globe, as remote as that of the cretaceous formation.
Strata older than Cretaceous.-At the time when I wrote my first paper on the geology of Texas, I had no knowledge of the existence in the country, of any strata older than the cretaceous deposits, except that there was a single rock of granite about fifteen miles northeast of Fredericksburg. But in the early part of this year, a short time before my leaving the country, I had a
* I saw a specimen of this species at Philadelphia, in the Museum of the Acad. of Natural Sciences, which has been brought from Green county, Alabama, by Mr. Conrad.
SECOND SERIES, Vol. VI, No. 16.—July, 1848.
very favorable opportunity to visit that section of country which lies between the Piedernales, Llano, and San Saba, (all three of them tributaries of the Colorado,) and which, on account of the dangerous character of the Indians by whom it is inhabited, has remained until now, almost entirely unknown. In this region, I found besides the cretaceous formation, not only an extensive tract of granite, and other crystalline rocks, but also stratified deposits, which from the fossils they contain, are clearly Silurian strata, and carboniferous limestone. In order to make the geographical distribution of these rocks distinctly understood, it will be necessary first, to point out the route which I took in the exploration of this region. Starting from Fredericksburg, a German settlement which is situated about ninety miles north of the town of San Antonio de Bexar, and about four miles from the Piedernales, we took a northwestern course, and followed it not only as far as the Llano river, but also beyond it, until we reached the San Saba. We then ascended the valley of this river about fifty miles, until we reached the San Saba, that is to say, beyond the ruins of the old Spanish fort, and within about eight miles of the sources of the river. From there, we went down the valley again, passed the point where we first struck it, and continued descending the valley, until we arrived at a camp of the Camanche Indians, about twenty-five miles from the mouth of the river. There we left the valley of the San Saba, and went back to Fredericksburg, in an almost exactly southern course. On this tour the following rocks were observed.
From the Piedernales to the Llano, the same cretaceous strata extend, which, consisting of a compact white, or yellowish limestone, with occasional nodules of flint, occupy likewise the whole tract of land from the Piedernales down to San Antonio and Austin. On the banks of the Llano, a calcareous sandstone distinctly stratified, but evidently much altered, begins to show itself; its extension, however, is only a limited one, for about five miles beyond the river it is superseded by granite. This latter rock, occupies almost the whole tract of country between the Llano and San Saba, and it is only on the dividing ridge of the last mentioned river, that limestone beds reappear again.
The granite is on the whole, coarse grained, and appears red from the color of the feldspar. It constitutes either large rocks with bold outlines, or flattened masses, which project only very little above the surface of the ground, and become visible mostly in the beds of several small streams, by which the country is intersected.
About ten miles from the place where we first entered the San Saba valley, on the right bank of the river, horizontal beds of limestone, of a decidedly Palæozoic character, were first met with. This limestone, of a grayish impure color and of a granular struc
ture, bears strong evidence of alteration by the action of heated plutonic rocks. This igneous action has not however obliterated all the organic remains of the limestone. Fossils, on the contrary, although not of many species, are abundant. Among them Trilobites are especially numerous. Those which I collected belong to the genera Asaphus and Bronteus. In specific characters they differ from many found in the valley of the Mississippi, or in other palæozoic strata of America. Besides these Trilobites, some indistinct species of Orthis were found at the same locality. Some miles further up this river, at a place where the limestone does not exhibit any marks of plutonic action, some other genera of fossils are met with, as for instance Euomphalus, Spirifer, etc. Of the latter genus one species was found which is closely allied to the Spirifer lynx, Eichw., a fossil shell so widely spread in the beds of Trenton limestone of the state of New York, and the corresponding strata of the western states. In ascending still higher the valley of the San Saba, we lost sight of all Palæozoic strata, cretaceous strata of the same character as those which we had seen before, taking their place at the surface, and occupying especially all the neighborhood of the old Spanish fort. We met Silurian strata again nearer to the mouth of the San Saba river. Here they consisted of a white siliceous limestone, evidently much altered, although not to such a degree as to destroy all marks of organic remains. A species of Euomphalus with a great number of whorls, analogous to a species from the Silurian strata of Russia, could be distinctly recognized. Still further down the river, and about thirty miles from its mouth, we found in the narrow valley of a tributary of the San Saba river, inclined strata of a dark colored compact limestone, with layers and nodules of black silex. These beds of limestone abound with fossils which evidently belong to the carboniferous period, and some of them are even exactly identical with species of the carboniferous limestone of the Mississippi valley. Most of the species which were observed in the very short examination of the locality, belong to the genera Productus, Spirifer, and Terebratula.
On our return from the San Saba to Fredericksburg, we crossed again the same belt of granitic rocks which we had seen previously after passing the Llano, and did not observe any cretaceous strata before reaching the dividing ridge of the Piedernales and Llano.
The main results of this journey, as well as of former investigations, may be more clearly exhibited in the following statements.
The immense tract of hilly or mountainous country extending from the Rio Grande to Red River, is mostly formed by strata of the cretaceous formation differing in their fossil fauna from the cretaceous deposits in New Jersey and in other localities on the Atlantic coast, but exhibiting a striking analogy with some of the cretaceous deposits in the south of Europe around the Mediterranean, in the same degree as those of the Atlantic coast are similar to the cretaceous deposits of England and northern Germany. Surrounded by these cretaceous deposits, there exists between the Piedernales and San Saba rivers, a belt of granitic rocks and of palæozoic strata. The latter are characterized by their fossils as Silurian strata and carboniferous limestone, both are different in their organic characters from the corresponding formations in the Mississippi valley, as might be expected considering the great distance and difference of latitude.
As a fact bearing on the geography of the western part of Texas, I will mention before concluding this paper, that the range of mountains which, under the name of the San Saba mountains, is laid down on some maps, does not exist. On either side of the San Saba river no elevation of any importance is seen above the general level of the table land.
The detail of my geological researches in Texas will be given in a more elaborate work. The publication of which will take place with the least possible delay.
Berlin, August, 1847.
ART. III.—On the Orbits of the Asteroids ; by
B. A. Gould, Jr., A.A.S. The recent discoveries of Hencke and of Hind, by which the number of small planets known to us between the orbits of Mars and Jupiter has been doubled, have directed the attention and interest of astronomers in a still higher degree to the group of these remarkable bodies.
By the common consent of astronomers, they have received the name of "asteroids," a name proposed by the elder Herschel, in consequence of a theory of his own. The word asteroid, in its present signification, may be defined as “a small planetary body, which revolves around the sun between the orbits of Mars and of Jupiter.”
Immediately upon the discovery of Pallas, the calculations of. Gauss showed that the orbits of Ceres and Pallas approach very near to one another in the descending node of Pallas upon the Ceres-orbit.
Upon this fact Olbers grounded his well known and not un natural hypothesis, that these two extremely small bodies, whose orbits approach one another so nearly in the node, were merely the fragments of a larger planet, which by some force unknown to us, had exploded or been shattered by some external shock.