ing the light peripheral zone and another situated at about one-third of the distance between the periphery and the umbilicus anterior to the periphery. Here, as in the banding of the upper surface, we find a considerable variation both as to intensity of coloration and width of the band. In some the zone at the periphery is merely indicated (Obba marginata lanaona and Obba marginata mearnsi), while in others they are very dark and broad (Obba marginata marginata and Obba marginata balutensis). In all the forms the basal lip is toothless. Under the microscope we find that the first half turn is smooth; the turn and a half following this are marked by slender oblique, retractively curved, axial threads, best seen near the summit and at the periphery; while the succeeding turns have in addition to these threads, very fine, closely spaced, impressed lines which cross each other more or less at right angles and the lines of growth at an angle of about 45° and give the surface a fine cloth-like texture. The various subspecies of Obba marginata can readily be divided into two groups, one in which the dark coloration predominates over the light zones and another in which the reverse is true. To the first of these, the dark group, belong the subspecies saranganica, balutensis, marginata, worcesteri, and boholensis. In the light group we find characters that readily enable one to further subdivide it. In two forms (mearnsi and palmasensis) the shell is broadly conic. In the rest the shell is lenticular. This last complex is again divisible. One part (subspecies griseola, samarensis, pallescens, and nana) has the basal peripheral band well developed. In the other (subspecies zamboanga, lanaona, and joloensis) the basal peripheral band is obsolete. The distribution, as known to date, extends from the central islands of Samar, Leyte, Bohol, and Cebu, southward over Mindanao to Jolo on the west and Sarangani and Palmas islands on the east in the Philippines, and still farther south beyond our range at least to Celebes. A plotting of the known distribution points strongly to the fact that many additional subspecies may be expected when more careful and extensive collecting shall have been done. The species should occur on the islands between Samar, Leyte, and Mindanao: In Mindanao itself we know it only from the northern coastal strip and Zamboanga and it scarcely stands to reason that there should be a gap in the distribution between the north coast and the little islands of Sarangani, Balut, Olanivan, and Palmas off the southeast coast where it is well represented. The distribution of the groups outlined above is rather interesting. The subspecies in which the dark coloration predominates are known from Bohol, Camiguin, north of Mindanao and the islands of Olanivan, Sarangani, and Balut off southeastern Mindanao. None of the dark forms so far are known from the large island of Mindanao itself. The broadly conic light-colored Obba marginata mearnsi and Obba marginata palmasensis come from Sarangani and Palmas, respectively, both off southeastern Mindanao. The light colored lenticular forms having the basal peripheral color band well developed are so far known from Samar, Leyte, Cebu, and northeastern Mindanao, and I strongly suspect that the form recorded from Siquijor and that from Talisayan, Mindanao, will prove to belong here. The light-colored lenticular forms in which the basal peripheral band is obsolete are known from western Mindanao and the island of Jolo. The following key may be of help in determining the known subspecies1: Dark bands predominating over the light zones. Greater diameter more than 30 mm. Lines of growth strongly developed (Sarangani Island). saranganica Hidalgo. Lines of growth not strongly developed (Balut Island). Greater diameter less than 30 mm. Greater diameter more than 25 mm. (Camiguin Island). Basal bands light brown (Bohol Island). Dark bands not predominating over the light zones. Peripheral basal color band moderately strong (Palmas palmasensis new. Peripheral basal color band obsolete (Sarangani Island). Shell not broadly conic, lenticular. Peripheral basal brown band obsolete. mearnsi new. Median band above and below reddish (Zamboanga, zamboanga new. 1 The types of the new subspecies are registered in the U. S. National Museum under the following numbers: balutensis, no. 256548; boholensis, no. 116914; palmasensis, no. 256420; mearnsi, no. 256423; lanaona, no. 256495; joloensis, no. 256549; samarensis, no. 256549. Median band above and below not reddish, all bands brown. Base very strongly convex (Lanao Province, Mindanao).. lanaona new. Base very slightly convex (Jolo Island). Peripheral basal brown band not obsolete. Band near the summit and at the periphery Greater diameter less than 21 mm. samarensis new. Peripheral basal band strong (Leyte Island). pallescens Möllendorff. Peripheral basal band not strong (Northeast ABSTRACTS Authors of scientific papers are requested to see that abstracts, preferably prepared and signed by themselves, are forwarded promptly to the editors. Each of the scientific bureaus in Washington has a representative authorized to forward such material to this JOURNAL and abstracts of official publications should be transmitted through the representative of the bureau in which they originate. The abstracts should conform in length and general style to those appearing in this issue. GEOLOGY.-Geology of the Navajo country. A reconnaissance of parts of Arizona, New Mexico, and Utah. HERBERT E. GREGORY. U. S. Geological Survey Professional Paper 93. Pp. 161, with maps, sections, and illustrations. 1917. The region bordering the Colorado canyons between Little Colorado and San Juan rivers and extending southward to the line of the Atchison, Topeka & Santa Fe Railway is described. The primary object of the investigations was to "spy out the land," with a view to suggesting ways in which the country could be more fully utilized. The region is arid, and the geologic field work was therefore designed chiefly to obtain information concerning the water supply. The Navajo country is part of the Colorado Plateau province, a region of folded and faulted sedimentary rocks traversed by innumerable canyons. The consolidated sedimentary rocks exposed in the Navajo country are chiefly of Mesozoic age-Triassic, Jurassic, and Cretaceous. The predominant rock of the whole Navajo country is sandstone of medium grain; limestone and conglomerate are much less common, and typical clay shale is rare. In the Grand Canyon district the dominating structural features are represented topographically by flat-topped plateaus, bordered by lines of displacement trending roughly north. The simplicity of folded structures in the Grand Canyon district is not, however, duplicated in the region east of Colorado River. Synclines and anticlines, both broad and narrow, sharply delineated monoclines, and domical upwarps follow one another in succession or abut against one another like waves in a choppy sea. In one feature only-their general trenddo the flexures displayed in the Navajo country simulate those of the region farther west. Ten major folds and eight minor folds, in addi tion to local flexures of small dimensions, were noted in the region. between the San Juan and the Puerco and Little Colorado. The physiographic history of the Navajo country is included in that of the Colorado Plateau. The stratigraphic series of the area is essentially that of the Grand Canyon district; the crustal movements of the two areas, though different in kind, were probably contemporaneous, and it is reasonable to suppose also that the periods of igneous activity for the whole Plateau province are closely related in time. The surface of the Navajo country has been carved rather than built; features resulting from deposition are relatively unimportant. Talus slopes and alluvial fans are replaced by cliffs; hills and knolls give way to buttes and towers; and graded slopes are represented by walls sculptured into rincons, recesses, alcoves, niches, windows, and arches, of large variety. Wide, open mouths of niches and caves perched high on the canyon walls are conspicuous. These cavities, protected from rain, from the glaring heat of the sun, and from the suffocating sandstorms, were widely utilized by the ancient inhabitants as building sites-"rock shelters" or "cavate dwellings." Perhaps the most striking erosion feature within the Navajo country is the recently discovered Rainbow Bridge, which spans Bridge Canyon, on the northwest slope of Navajo Mountain. Its symmetry and graceful proportions, as well as its size and beauty of color, give to this arch a commanding position among the natural bridges of the world. R. W. STONE. GEOLOGY.-Ground water for irrigation in Lodgepole Valley, Wyoming and Nebraska. OSCAR E. MEINZER. U. S. Geological Survey Water-Supply Paper 400-B. Pp. 33, with 4 maps. 1917. This brief report discusses the distribution and water-bearing character of the Ogalalla and Arikaree formations, the Brule clay, the underlying formations, and the Quaternary stream gravels. Large yields are obtained in the valley from the stream gravels and from the underlying jointed portions of the Brule clay. The strongest well yielded, in a test of one hour, at the rate of 710 gallons per minute with a drawdown of less than 4 inches. The report describes the natural processes of storage of water in the underground reservoir and of discharge therefrom by gravity in the irrigation season. It also gives data by the author and by Mr. H. C. Diesem, of the Department of Agriculture, on the cost of pumping for irrigation. O. E. M. |