« ΠροηγούμενηΣυνέχεια »
In the field, the geologist scrutinizes every inch of these sands and clays, and upon finding so much as a tooth exposed to view it is carefully examined and if there are signs of a skull or mandible, either in whole or in part, or any other good bone, the picks, spades, and drills are set to work digging out a large block of the matrix in which the specimen is embedded, the matrix being the best packing material in which to ship a specimen. If much of the fossil is exposed, paper, or sometimes cloth, is pasted over it, and if it is a very heavy bone, and unusually choice, paper, cloth, and burlap are successively pasted upon it. Care is used not to cook the paste, but to make a very thick batter of flour and water. The whole, when dry, is stiff as a board, and the fossil is ready for a journey of any distance. Sometimes a thin coating of plaster of Paris may be added over all to advantage.
When beginning work on these specimens in the laboratory, the paper or cloth is soaked and pulled off, then the task of removing the matrix begins. This matrix or sandstone is of all degrees of coherence, varying from the friable to that of flinty hardness. As the matrix varies from soft to hard, so the fossils incased will vary in hardness.
The chisel and mallet are among the most useful tools in this work, with awls of different kinds for the more delicate bones; trowels, chisels, scrapers, and penknife for the larger bones. The sand bag, upon which the matrix rests while we dig out the specimen, and the sand box, in which one part of the specimen can be firmly supported while the other parts are attached, are indispensable to the workroom.
We will suppose the matrix removed and all ready for joining the parts cracked by.frost, or broken while removing the hard sandstone. The very small bones can be safely united with glue. The next larger sized bones can be satisfactorily fastened together with plaster of Paris, using gum-water instead of water for making the plaster. The plaster made with gum acacia, dissolved in water, has many advantages over the ordinary plaster, as it does not harden so soon, and more time and care can be used in joining the breaks; and when this plaster is once set it is much
harder and more lasting than the ordinary kind. True, the gum acacia is expensive, but if used with care, a little will last a long time, and it has many useful qualities. Glue water has much the same effect, but is not quite so satisfactory, and, if used freely, causes the plaster to crack.
And now come the large bones of the large animals. These are much more difficult to join than the small and medium-sized bones which we have just been considering. In the hollow limb bones, the outer portions are often hard and durable, while the cavities are filled with calcareous material which can easily be bored. Taking care that the holes in the pieces to be joined correspond, insert long screws or wire and fill in with plaster of Paris, thus making a strong joint. Again, the cavities may be filled with material so hard that hydrochloric acid is used to eat out the holes.
The Loup Fork Tertiary, which extends through the western part of this state and down into Kansas, is a more recent deposit than the Bad Lands, so the bones found at Long Island, Kan., where the Morrill Geological Expedition collected one summer, are very brittle, as the organic matter has been removed and the cavities have not been filled. Hence exposure to the air often causes such bones to crumble. At best they are very delicate specimens to handle, but they can be hardened by soaking in gum water or glue water and drying.
In the loess, which is our most extensive deposit and a very recent one, many fossils are found, which must be treated in a similar manner.
Although western Nebraska is in the distinctly sub-arid and "arid” regions, yet there is no part of the state so arid that tuft grass instead of prairie grass grows. This tuft grass is a distinct characteristic of the extreme arid region. In such regions it is rather a simple matter to find exposed on the surface between the tufts of grass such bones as may be washed out by storms and freshets; however, in Nebraska it is a much more complex matter to find such' remains, because of the covering of grass which practically grows over the whole state, save in the very bad lands
themselves. However, if such fragile bones as those of the mastodon and mammoth—which have been so recently buried that they are rendered brittle by the loss of their organic matter, without replacement by calcium carbonate or silica-were exposed on the surface they would perish immediately. Accordingly those preserved have generally been brought to light by the plow and scraper in preparing some cut or fill for the railroad or public highway or for an irrigating ditch. In other cases the farmers notice around the prairie dog holes stray bits of bones, which, from their very texture, show that they are of organic origin, and so arouse attention. By following the holes a sufficient distance, the bones through which they burrowed can be rescued. In this way, by following the windings of a prairie dog burrow for nearly forty feet through the loess formation in Buffalo county, one of the tusks in the State Museum was recovered, together with fragments of other bones. The particularly fine pair of tusks, which are scarcely rivalled by any better representatives in any museum, were found in a railroad cut along the Burlington and Missouri River railroad in Gosper county.
At this particular spot the loess is very thick, and being subject to considerable surface erosion, it is cut in all directions by various drainage lines, so that the whole region is crossed by rather sharp draws, bordered by hills of yellow bluff soil. The railroad made a cut through one of these hills amounting to several hundred yards in length, and from fifty to sixty feet in depth. The material excavated in the cut was shipped forward a distance of a mile or two to make an extensive fill. The workmen said that "they had never plowed and scraped through such remarkable bones.” The scraper and plow cut through thigh bones, vertebrae, ribs, scapula, and skull, bringing them to the surface where they were much admired for their size and beauty, but for all that they were carried to the dump and forever destroyed. The plow and scraper went mercilessly and merrily on, until it had entirely destroyed the skeleton, the skull, and two to three feet of the great tusks. But the work of destruction was not to end there, for the workmen after that amused themselves
by reaching in at the side of the bank and pulling out handsful of the friable bony matter of the tusk. This being incompletely fossilized, and having been subject to the action of frost and the force of growing rootlets, was shattered into innumerable small bits, so that the once hard ivory could now be picked away by the handful. Every scrap of tusk was entirely picked away as far in as the arm could reach. The work of destruction would have gone still farther if it had not involved some labor. The railroad men reported this specimen to a local doctor, who immediately decided to rescue the tusks for his private collection; accordingly he dug quite a ditch in such a way that it would cross about the middle of the left tusk. It may be explained here that the two tusks laid quite as they did in life. At this point he cut out as much as he could without broadening his ditch; finding it was simply so many fragments in his hands, it occurred to him that very likely the tusk was more solid at the tip. Accordingly he dug a second trench near the tip, and there destroyed nearly three feet more of this excellent specimen. Fortunately, while he dug away everything else, he did leave the hole where the tusk laid; accordingly it was not a very difficult matter to fill in these places with plaster of Paris, and so preserve with actual fidelity the shape, size, sweep, and length of the tusk. The holes in the bank where they had reached in and dragged out handsful of the ivory had suffered very little from several months of the weathering; these were likewise filled with the plaster of Paris and then the work of excavation began. They were overlaid by about five or six feet of the loess, which is soft and extremely easy to dig with the spade or shovel. However, during the entire time of excavation a fierce gale of wind was blowing, which carried so much fine sand that it was with extreme difficulty that the work could be carried on. As soon as a surface was laid bare on the tusk the wind immediately carried away pieces of the ivory—which was arranged in concentric layers; accordingly it was necessary not to expose more than two to three square inches at a time and to promptly paste over this a layer of paper, then expose a few inches more and paste that with
paper. In this way both tusks were dug out and laid bare to the action of the sun and wind. This done, it was found necessary to paste cloth over the tusks and around them in all directions, so as to give it sufficient "body" to hold the fragile parts in place until it could be shipped. Both tusks were allowed to stand on stilts of the original clay in which they were imbedded, but these had to be replaced by wooden stilts, in order that all of the surface might be pasted with paper, cloth, and burlap. The next thing was to pull up large masses of stiff grass, which grew in a marshy spot near by. These tufts of grass were arranged longitudinally along the tusks and wrapped and tied very securely in place by means of binding twine. On top of all was bound a heavy layer of stout willow sprouts in order to give it additional stiffness and strength. However, in spite of all these precautions, it was found to be entirely impracticable to lift or move these tusks in any way. The only possible means of rescuing them was to build a large crate about them as they lay in position and to suspend each tusk by means of rope and twine. In this position, when sufficiently roped, it was an easy matter to pick up crates and specimens and carry them down the hill and deliver them at the nearest station, some nine or ten miles distant. The boxes when done were so large that it was found impossible to get them inside of an ordinary wagon and considerable embarrassment was experienced for a time. Finally, however, they were roped on top of the wagon, extending across it, and in this way were transported safely to their destination. The tusks were driven across a very rough prairie, part of it without roads or trails, a distance of nine or ten miles, then shipped by railroad from Gosper county to Lincoln, and delivered at the museum still swinging by cords and ropes and without breakage or injury. Then began the work of unpacking and preparing the specimen in some permanent way. The burlap, cloth, and paper were removed, a few inches at a time, and a mixture of paraffine, beeswax, and resin was melted and poured over the exposed part. This melted mixture sank into every crack and upon cooling hardened and united the parts completely. Finally, holes were bored