Cultivated mind is the guardian genius of democracy.... It is the only dictator that freemen acknowledge and the only security that freemen desire.
Mirabeau B. Lamar
FOSSIL ICE CRYSTALS
By J. A. Udden
AN INSTANCE OF THE PRACTICAL VALUE OF "PURE SCIENCE"
The practical value of the service of the geological profession is, with every year, being more and more appreciated, especially among people who are developing the mineral resources of our country. Nevertheless, we still hear men who speak of geologists as theorists that render our profitable industries but little assistance. It is true that much of the work that geologists do has but a remote bearing on practical questions. The fact is that in geology, as in other sciences, one can never know when a purely scientific observation may turn out to have a practical application. Paleontologists who study the minutest details of fossils have been held up as impractical people, even though their science has more than once proved to be of the greatest practical importance for the finding of valuable natural deposits. Certainly those who have been most prominent in the promotion of paleontology as a science have seldom, if ever, had any economic motive in the pursuit of their work. I think the same is true of our leading petrographers. I believe that the men who have advanced the science of geology most, have seldom contributed much to the practical application of the principles they have discovered. Much scientific work naturally appears unprofitable or useless to the uninitiated. I shall here relate a case that suggests how entirely wrong it may be to regard as of no economic value any geologic fact, however insignificant it may appear.
In the summer of 1890 I took occasion to make a trip to the Black Hills in South Dakota in order to profit, as I could, by a few weeks' tramping in this interesting region. Going one day in a southwest direction from Minnekahta, to look for fossil cycads, I stumbled on a block of sandstone with a rather smooth surface on which were some peculiar markings, such as I had never seen figured or described. The rock was evidently a block from the Dakota sandstone. Its smooth upper surface, which represented a bedding plane, was covered with a thin coating of silt or fine clay which adhered to the block. The markings were in this clay. They were straight, shallow grooves from one-half to two inches in length, and from one-sixteenth to one-eighth inch in width. They were joined into patterns in which some sprang out from the sides of others and again themselves sent out other branches. Some crossed each other. I noticed that there was a quite uniform angle of divergence in these branches, and I was able to make out that this usual angle was about sixty degrees. I also noted that the grooves narrowed to sharp points. Somehow, immediately I concluded that the cracks were the result of ice crystals, and I at once saw the propriety of frozen water having existed in an age during which deciduous trees began to appear. This was theory. We have since that time learned to know that cold climates far antedate the coming of the dicotyledons.
As I had no suitable photographic equipment, I took pains to make accurate drawings of a part of the pattern as it appeared on the rock. My original drawing is shown in [Plate I]. A brief description of these markings was later furnished in the Scientific American, of February 19, 1895.
It took me some years to find any similar markings again. In the early spring of 1903 I had occasion to make a visit to Mexico, when I spent a half day in Ojinaga, which is a little village south of Presidio, in Texas, on the Mexican side of the river. Some sidewalks in this little village are built of flags of limestone belonging to the Eagle Ford formation. To my great delight I found some of these slabs having precisely the same kind of markings that I had noted on the sandstone in Dakota. Naturally I attached some importance to the fact that the Eagle Ford corresponds quite closely in age to that of the Dakota sandstone. Both were made at about the beginning of the upper Cretaceous age. I noticed here a considerable variation in the closeness of the patterns of the markings. Occasionally they were found as separate single lines, several inches removed from each other; and on other rocks they would be found crossing in close networks. In the summer of 1904 I again found my ice markings on a layer of arenaceous limestone in the same formation in the Big Bend country in Texas. This time I collected some specimens which were subsequently photographed. One of these photographs is shown in [Plate II]. Again in 1906 I noticed the same markings on some thin sandy flags which occur in the Del Rio clay near the city of Del Rio. In this case the needle-like crystals were somewhat more slender than those previously seen, and some were slightly curved and somewhat more elongated. These of course interested me as showing the occurrence of freezing temperatures no doubt at a somewhat earlier time than that pertaining to my previous observations.
During all these years my residence was in Illinois, and I was naturally watching for similar markings in recent mud, resulting from late and early frosts. I found them in the fall of 1909. At this time some excavations were being made in the loess in Rock Island, when some rains fell in the late fall. These rains evidently happened to give the mud the amount of moisture necessary for such crystals to develop, as the ground froze. The rains had washed the loess extensively, and I found a number of places where it lay redistributed, with a fairly smooth surface. It was evident that the moisture content of the ground, together with the temperature conditions, determined the size and the closeness of the frozen patterns. In places the crystals were long and slender, in others they were short and stout. At some points they were straight and in others slightly curved. Here and there the patterns were close enough to resemble the fine lines which we sometimes notice in the hoarfrost on windowpanes. In other places the crystals occurred in radiating groups, and elsewhere they would form scattered separate units. For preserving a record of what I saw, I poured plaster over several patterns and had these casts photographed, as appears in [Plates VIII], [IX], [X]. Placing these side by side with the photographs of the patterns I have photographed from the Eagle Ford, it appears to me that no doubt can be left as to the origin of the markings found in the fossil state.