Imágenes de páginas
PDF
EPUB

what fully. In speaking of the horned dinosaurs in the publication just cited he says: “The geological deposits, also, in which their remains are found have been carefully explored during the past season, and the known localities of importance examined by the writer, to ascertain what other fossils occur in them, and what were the special conditions which preserved so many relics of this unique fauna.

“The geological horizon of these strange reptiles is a distinct one in the upper Cretaceous, and has now been traced nearly eight hundred miles along the eastern flank of the Rocky Mountains. It is marked almost everywhere by remains of these reptiles, and hence the strata containing them may be called the Ceratops beds. They are freshwater or brackish deposits, which form a part of the so-called Laramie, but are below the uppermost beds referred to that group. In some places, at least, they rest upon marine beds which contain invertebrate fossils characteristic of the Fox Hills deposits.” Italics mine.

If we accept literally Marsh's statement that the Ceratops beds have been traced for eight hundred miles along the eastern flank of the Rocky Mountains, it will be necessary to suppose that he includes in the Ceratops beds not only the beds in Converse Co., Wyoming, but also the Bison beds (Denver beds of Cross) at Denver, and the Judith River beds on the upper Missouri. These are very widely separated localities, and no attempt has ever been made to trace the continuity of the strata from the one to the other, nor is it at all probable that such an attempt would meet with success. Professor Marsh did in the autumn of 1889 spend nearly two days in the Converse Co. locality, and again in 1891 he spent one full day in the same locality; but his time was occupied in visiting a few of the localities in which dinosaur skulls and skeletons and Laramie mammals had been found. No time was taken to determine the upper and lower limits of the beds or to trace the outcrops of the strata. After his visit in 1889 when he spent nearly two days with our party in the Converse Co. locality, he took the train for Denver, and in the company of Mr. George L. Cannon of that city, he spent one-half day examining the Bison beds (Denver beds). This constitutes Professor Marsh's field work in the Ceratops beds. In a total of three and one-half days field work he seems to have found sufficient time to “carefully explore " the geological deposits of the Ceratops beds and to trace them for “eight hundred miles along the eastern flank of the Rocky Mountains,” besides making numerous other observations of scientific interest.

Of the many interesting vertebrate fossils described by Professor Marsh from the Ceratops beds, those from the Denver locality were secured by Messrs. Cross, Eldridge and Cannon, and those from Wyoming and Montana by the writer or men in his party, with one exception only, namely, the type of Hadrosaurus breviceps, which was received at New Haven many years ago, the locality on the label accompanying it being given as Bear Paw Mountains, Montana, which is of course incorrect, it doubtless is from the vicinity of Cow Island. With this one single exception I can confidently state that all the material described by Professor Marsh as from the Laramie or Ceratops beds of Wyoming is, without exception, from Converse Co., and was found within an area not exceeding fifteen miles in width from east to west by thirty miles in length from north to south; and all the material described by him as from Montana, with the one exception mentioned, was found on the Missouri River between the mouth of Arrow Creek, just above Judith River, and the mouth of Cow Creek, some fortyfive miles below, and never back farther than ten miles from the Missouri. It will thus be seen that the actually known area of the Ceratops beds is indeed very limited, and from these areas we should exclude certainly, the Judith River or upper Missouri and very likely the Black Butte locality in south western Wyoming. The beds of the former certainly and those of the latter almost certainly, belong to an older horizon than those of the Denver or Converse Co. localities; the latter may be considered as the typical locality for the Ceratops beds. All of the dinosaurs from the Judith River country are smaller, less specialized forms than those from the Converse Co. and Denver localities, as has already been observed by Marsh..

Marsh's statements that the Ceratops beds are below the uppermost beds referred to the Laramie and that they rest upon marine beds which contain invertebrate fossils characteristic of the Fox Hills deposits, may well be questioned, especially if we exclude from the Ceratops beds the Judith River beds and refer them to a lower horizon, retaining for them the name Judith River beds. · At no place in the Converse Co. region do the true Ceratops beds, with remains of horned dinosaurs, rest upon true marine Fox Hills sediments; nor are the Ceratops beds in this region overlaid by strata which could be referred without doubt to the Laramie. The writer has, in a paper published in the American Journal of Science of February, 1893, stated that the Ceratops beds rest directly upon the Fox Hills series, and has provisionally referred the very similar series of sandstones and shales conformably overlying the Ceratops beds to the upper Laramie; but it would doubtless be better to restrict the limits of the Ceratops beds to those strata in which horned dinosaurs occur, and to consider the underlying 400 feet of barren sandstones as the equivalent of the Judith River beds. Future investigations will doubtless show that the sandstones, shales and lignites overlying the typical Ceratops beds in Converse Co. should be referred to the Fort Union beds and not to the Laramie, as, according to Knowlton, the limited flora sent him now indicates.

The terms Fox Hills and Laramie as now used cannot be taken to represent distinct and different periods of time. for as has been shown by G. M. Dawson, Selwyn and McConnell in the Belly River region in Canada, and frequently observed by the writer on the upper Missouri in Montana, marine beds with typical Fox Hills fossils have been found interstratified with fresh and brackish water beds containing characteristic Laramie fossils, showing conclusively that the two periods were in part at least contemporaneous; the one representing the marine and the other fresh or brackish water forms existing at the same time and in not widely separated regions, these alternations in the nature of the fauna in the same locality having been brought about by successive encroachments and recessions of the sea. It is not at all impossible that in the region of Converse Co., Wyoming, marine conditions prevailed continuously until late in Laramie times, and that during the time of the deposition of the Laramie beds of the Judith River and Black Butte localities, marine beds with Fox Hills types of fossils were being deposited over the region of what is now eastern and central Wyoming. This would account for the absence in this region, of the lower Laramie, with the smaller and less specialized horned, and other dinosaurs, characteristic of it.

Other Localities for Horned Dinosaurs.

In addition to the localities already mentioned, the writer. has seen remains of horned dinosaurs and Hadrosauridæ on the North Platte River opposite the mouth of the Medicine Bow, about 35 miles below Fort Steele, Wyoming; along the eastern flank of the Big Horn Mountains about 40 miles south of Buffalo, Wyoming; on the west side of the Big Horn River between Fort Custer and Custer Station, Montana; and on Willow Creek 13 miles north of Musselshell postoffice in Montana. Another region not examined, but which looked very promising, is near the town of Havre on the Great Northern Railroad just north of the Bear Paw Mountains in northern Montana.

Suggestions to Collectors.

Of all the localities for Laramie dinosaurs and mammals known to the writer, that of Converse Co., Wyoming, is by far the most promising, and the earnest and intelligent collector will there meet with a fair amount of success for many years to come. As will be seen, by reference to the map accompanying this paper, this region is easy of access from the town of Lusk on the F. E. and M. V. R. R. At this station all necessary camp supplies can be obtained. The fossil beds are easily worked, the country being quite open and its surface not disfigured by deep and impassable cañons. There is abundant grass for horses, wood for fuel, and frequent small springs of fairly good water.

Vertebrate fossils are never abundant in the Laramie, but every exposure in this region should be carefully searched and especially the large sandstone concretions which contain many of the best skulls and skeletons found in these beds. Fossils are found in both the shales and sandstones, but are best preserved in the latter. The small mammals are pretty generally distributed but are never abundant, and on account of their small size are seen with difficulty. They will be most frequently found in what are locally known as “blow outs” and are almost always associated with garpike scales and teeth, and teeth and bones of other fish, crocodiles, lizards and small dinosaurs. These remains are frequently so abundant in “ blow outs” as to easily attract attention, and when such a place is found careful search will almost always be rewarded by the discovery of a few jaws and teeth of mammals. In such places the ant hills, which in this region are quite numerous, should be carefully inspected as they will almost always yield a goodly number of mammal teeth. It is well to be provided with a small flour sifter with which to sift the sand contained in these ant hills, thus freeing it of the finer materials and subjeeting the coarser material remaining in the sieve to a thorough inspection for mammals. By this method the writer has frequently secured from 200 to 300 teeth and jaws from one ant hill. In localities where these ants have not yet established themselves, but where mammals are found to be fairly abundant it is well to bring a few shovels full of sand with ants from other ant hills which are sure to be found in the vicinity, and plant them on the mammal locality. They will at once establish new colonies and, if visited in succeeding years, will be found to have done efficient service in collecting mammal teeth and other small fossils, together with small gravels, all used in the construction of their future homes. As an instance of this, I will mention that when spending two days in this region in 1893, I introduced a colony of ants in a mammal locality, and on revisiting the same place last season I secured in a short time from the exterior of this one hill 33 mammal teeth.

Another way to secure these small teeth is to transport the material to a small stream and there wash it in a large sieve in the water, the finer material being washed away, but this treatment is too harsh to give the best results, what few jaws there are always being broken to bits.

« AnteriorContinuar »