A very strong blue line, having a fainter line on each side, forming a close triplet. It is a prominent line in all the samples of gas examined. Young gives the wave-length 44718 for a line in the chromosphere, and Lockyer gives 4471 for a line in gas from bröggerite. Seen in "helium puriss." Young gives a chromospheric line at 4437-2. (These two lines form a close pair. I can only see them in "uraninite, R." No trace of them can be seen in the gases from other sources. Young gives chromospheric lines at 4426.6 and 4425 6. A strong line, only seen in "uraninite, R." Absent in the gas from the other sources. Lockyer gives a line at 4398 in gas from certain minerals. Young gives a chromospheric line at 4398.9, Seen in all the samples of gas. Young gives a These two lines form a pair seen in " uraninite, Only seen in "uraninite, R." chromospheric line at 4298.5. Only seen in "uraninite, R." Young gives a The strong head of a nitrogen band occurs close to the line. Seen in all the samples of gas. Only seen in "uraninite, R." Only seen in "uraninite, R." Young gives a chromospheric line at 4226 89. (These three lines form a prominent group in An extremely faint line. Lockyer gives a line Present in all the gases except These lines form a very close pair, seen in all 4026.5. Seen in all the samples of gas. 66 The center line of a dense triplet. Only seen in Seen in all the samples of gas. Very strong in "uraninite, R," very faint in clèverite, R," and not seen in the others. Lockyer finds a line in gas from bröggerite at 3947. There is an eclipse line at the same wave-length. Seen in "helium puriss." Seen in "helium puriss." Only seen in "uraninite, R," and 3913.5. "helium Hale gives a chromospheric line at A very strong triplet, seen in all the samples of gas. Lockyer finds a line having a wave-length 3889 in gas from bröggerite. Hale gives a chromospheric line at 3888.73. There is a strong hydrogen line at 3889.15. Only seen in "uraninite, R." Seen in "helium puriss.' Seen in all the samples of gas. Deslandres gives a chromospheric line at 3819.8. Seen in "helium puriss." Seen in "helium puriss." Hale gives a chromospheric line at 3733.3. Seen in all the samples of gas. Deslandres gives a chromospheric line at 3705'9. 3890.5 9 3888.5 10 3885.9 9 3874.6 6 3867.7 3819.4 8 10 3800.6 3732.5 5 3705'4 6 3642.0 Seen in "helium puriss." Only seen in "uraninite, R." Seen in "helium puriss." The center line of a close triplet. Very faint in "clèveite, R," and "uraninite, R," and strong in "helium puriss." and in "bröggerite, L." It is not seen in "bröggerite, R." Wave-length. Intensity. A prominent line, only seen in "helium puriss." and in "bröggerite, L." Seen in "helium puriss." A mercury line occurs 2536 72. Seen in "helium puriss." Seen in "helium puriss." 2419.8 2 Seen in "helium puriss." Some of the more refrangible lines may possibly be due to the presence of a carbon compound with the helium. To photograph them a long exposure, extending over several hours, is necessary. The quartz window has to be cemented to the glass with an organic cement, and the long-continued action of the powerful induction current on the organic matter decomposes it, and fills the more refrangible end of the spectrum with lines and bands in which some of the flutings of hydrocarbon, cyanogen, and carbonic anhydride are to be distinguished. There is a great difference in the relative intensities of the same lines in the gas from different minerals. Besides the case mentioned by Professor Kayser of the yellow and green lines 5876 and 5016, which vary in strength to such a degree as to render it highly probable that they represent two different elements, I have found many similar cases of lines which are relatively faint or absent in gas from one source and strong in that from another source. Noticing only the strongest lines which I have called "intensity 10," "9," or "8," and taking no account of them when present in traces in other minerals, the following appear to be special to the gas from uraninite : The following strong lines are present in all the samples of The distribution assigned to some of the lines in the above tables is subject to correction. The intensities are deduced from an examination of photographs, taken with very varied exposures; some having been exposed long to bring out the fainter lines, and some a short time to give details of structure in the stronger lines. Unless all the photographs have been exposed for the same time, there is a liability of the relative intensities of lines in one picture not being the same as those in another picture. Judgment is needed in deciding whether a line is to have an intensity of 7 or 8 assigned to it; and as in the tables I have not included lines below intensity 8, it might happen that another series of photographs with independent measurements of intensities would in some degree alter the above arrangement. In the following table I have given a list of lines which are probably identical with lines observed in the chromosphere and prominences: * A Treatise on Astronomical Spectroscopy, by Dr. J. Scheiner, translated by E. B. Frost, Boston, 1894. The wave-lengths to which the initials D. and H. are added are wave-lengths of lines photographically detected in the spectrum of the chromosphere by Deslandres (D) and Hale (H). Their photographs do not extend beyond wave-length 3630. Professor Lockyer (Roy. Soc. Proc., vol. lviii, p. 116, May, 1895) has already pointed out fourteen coincidences between the wave-lengths of lines in terrestrial helium and in those observed in the chromosphere, the eclipse lines, and stellar spectra. ART. XXXIV.-On the Igneous Rocks of the Sweet Grass Hills, Montana; by W. H. WEED and L. V. PIRSSON. IN northern Montana, the broad expanse of the great plains that lie east of the Rocky Mountain Cordillera is interrupted by a group of peaks, rising abruptly from the general level near the Canadian boundary line. These peaks, forming three isolated mountain masses, are known as the Sweet Grass Hills, or Three Buttes. Their sharp outlines and isolated position attract attention from every point of view, while recent discoveries of copper leads and ores of the precious metals, together with the excellence of the coal beds upon their flanks, have caused an influx of prospectors from the mining regions of the state. The locality is now easily reached, as a tri-weekly stage runs from Shelby junction, where the Great Falls and Canada road crosses the Great Northern Railway, to the settlements on Birch Creek. The East and West Buttes are twenty miles apart, the Middle Butte lying to the south about midway between. The summits reach a height of 3,000 feet above the plains, and each butte is the center of a small mountain area whose verdure-clad slopes, copious springs and flowing streams are in strong and pleasing contrast to the desolate monotony of "Lonesome" prairie to the south. Through the kindness of Dr. G. M. Dawson, Assistant Director of the Canadian Geological Survey, who is the only geologist that has explored the Hills, the authors have been allowed to examine a number of specimens of the volcanic rocks constituting the central cores of these interesting mountain masses. The general geology of the Sweet Grass Hills has been described by Dr. Dawson,* from whose report the following notes have been taken. The three buttes constituting the Sweet Grass Hills occur in the center of a broad and low anticlinal uplift that stretches for many miles parallel to the Rocky Mountain front, from which it is separated by a broad, shallow, synclinal basin. Each mountain mass consists of a core of igneous rock surrounded by Cretaceous beds uptilted at high angles, whose inclination gradually becomes less and less away from the eruptive rock, merging into the horizontal strata of the plains. The igneous rocks forming the central masses of these mountains, though very dense and compact, are seldom seen in solid masses, since they break readily into irregular, angular fragments from a few inches to two feet across, forming debris * Report Canadian Geol. Survey, 1882-4, C, pp. 16, 45. "Report upon country in vicinity of the Bow and Belly rivers, Northwest Territory." AM. JOUR. SCI.-THIRD SERIES, VOL. L, No. 298.-OCTOBER, 1895. |