for a knowledge of the field relations of the specimens studied. Messrs. Herrick, Clarke and Deming' have also studied a few specimens of the gabbro, both ordinary and orthoclastic varieties, from Duluth, but they have added little to what was already known concerning them, except the suggestion of the possible dependence of the orthoclase-bearing varieties upon their environment for the peculiar characteristics which they possess. The Canadian geologists have likewise been engaged in a study of the rocks on the north side of Lake Superior. Many allusions have been made to the massive sheets and dykes in the Thunder Bay region, but no microscopical descriptions of them have been published, with the exception of a few notes by the present writer appended to a report by Mr. Ingall on Mines and Mining in the Thunder Bay Silver District. In this report the relations of the large dykes and thick beds of diabase or gabbro to the fragmental rocks of the Animikie series north of the lake are carefully sketched, and the microscopic features of the most important rocks are described. In the Appendix,3 a few altered gabbros and diabases from both sheets and dykes are very briefly characterized. The former of these have the general peculiarities of the gabbro from the great dyke on Pigeon Point, Minnesota, referred to by the writer in an article on certain contact phenomena at this place, and described at greater length 5 in a bulletin of the U. S. Geological Survey. In the first of these two papers, in addition to the reference to the Pigeon Point dyke, a few remarks are made concerning the relations of Irving's orthoclase-gabbros to the more common varie 'C. L. HERRICK, E. S. CLARKE and J. L. DEMING: Some American Norytes and Gabbros. Am. Geol., June, 1888, p. 339. 2 E. D. INGALL: Report on Mines and Mining on Lake Superior. Geol. and Nat. Hist. Survey of Cannda. Montreal, 1888. 3 W. S. BAYLEY: Notes of Microscopical Examination of Rocks from the Thunder Bay Silver District. 4 W. S. BAYLEY: A Quartz-Keratophyre from Pigeon Point and Irving's AugiteSyenites. Am. Jour. Sci. XXXVII., 1889, p. 54. 5 W. S. BAYLEY: The Igneous and other Rocks on Pigeon Point, Minnesota, and their Contact Phenomena. Bull. No. 109, U. S. Geol. Survey, 1893. ties of the gabbro of the region, but no detailed descriptions of these rocks, nor of the ordinary gabbros, whose modified forms they are supposed to be, are given. Finally, Dr. A. C. Lawson' has mentioned some of the characteristics of certain diabases from dykes in the Archæan rocks of the Rainy Lake region, in which the gabbroitic as well as the diabasic structures are well exhibited, the former toward the centers and the latter near the sides of the masses. 2 The most comprehensive treatment of the "greenstones" and "greenstone schists" of the Lake Superior region is that by Dr. G. H. Williams in his bulletin on the origin of the green schist, supposed to underlie the Huronian in Michigan. In this volume the author not only describes the petrographical features of the schists with which he deals, but he likewise describes in some detail the microscopical characteristics of the diabases, diabase porphyrites, diorites, diorite porphyrites and gabbros, associated with the schists, and from some of which the latter have been derived. Within the past three years a number of papers have appeared in which reference is made to some of the special features of a few of the coarse basic rocks, both north and south of the lake, but no articles have been published that deal with their general features. Fairbanks 3 has communicated a few notes on the diorites and gabbros in the province east of the north side of Lake Superior. Irving and Van Hise have given a brief synopsis of the characteristics of the diabase dykes and interbedded sheets in the Penokee iron series on the south side 1A. C. LAWSON: Notes on Some Diabase Dykes of the Rainy Lake Region. Proc. Can. Inst. for 1887, and Report on the Geology of the Rainy Lake Region. Pt. F., Ann. Rep. Geol. and Nat. Hist. Survey of Can. for 1887-88, pp. 57-73 and 147-164. 2G. H. WILLIAMS: The Greenstone Schist Areas of the Menominee and Marquette Region of Michigan. Bull. No. 62. U. S. Geol. Survey, 1890. 3 H. W. FAIRBANKS: Notes on the Character of the Eruptive Rocks of the Lake Huron Region. Amer Geologist, I. 1890, p. 162. 4 R. D. IRVING and C. R. VAN Northern Wisconsin and Michigan. Chap. VII., The Eruptives. HISE: The Penokee Iron-bearing Series of I of the lake, and of the gabbro, diabases, diorites, melaphyres and porphyrites of the Keweenawan overlying the Penokee series to the north, while Hall has described a few hand specimens of diabases and gabbros from the Archæan of Central Wisconsin. Further, in a discussion as to the nature of the diabase sheets interbedded with the Animikie slates and quartzites in Minnesota and Canada, which leads to the conclusion that the former are subsequent intrusions between the clastic beds, Lawson 2 gives a short generalized description of the petrographical characteristics of these rocks, and in a second article 3 he treats of the structure and composition of the anorthite rock of Irving, to which he gives the name anorthosyte. Finally, the writer in two articles refers to the coarse gabbro of north-eastern Minnesota and to the peridotites and pyroxenites 5 associated with it along its northern border. W. S. BAYLEY. 'C. W. HALL : Notes of a Geological Excursion into Central Wisconsin. Bull. Minn. Acad. Nat. Sciences, III., No. 2., p. 251. 2 A. C. LAWSON: The Laccolitic Sills of the Northwest Coast of Lake Superior. Bull. No. 8, Geol. and Nat. Hist. Survey of Minnesota, p. 30. 3 A. C. LAWSON: The Anorthosytes of the Minnesota Coast of Lake Superior Ib., p. 2. 4 W. S. BAYLEY: A Fibrous Intergrowth of Augite and Plagioclase, resembling a Reaction-rim, in a Minnesota Gabbro. Amer. Jour. Science, XLIII. 1892, p. 515. 5 W. S. BAYLEY: Notes on the Petrography and Geology of the Akeley Lake Region, in North-eastern Minnesota, 1892, p. 193. A STUDY IN CONSANGUINITY OF ERUPTIVE ROCKS. WITHOUT being distinctly formulated, the principle of consanguinity recently enunciated by Prof. Iddings has, as a working hypothesis, been the guide of studies made within the last few years on a group of Brazilian eruptive rocks, and the means of arriving at some interesting and, in part, novel results. The method of study followed, partly by plan, partly from force of circumstances, being the comparative study of a group of localities on the assumption of genetic relations between them, rather than detailed work at single points, was similar to what would be applied to the study of a sedimentary group. This method has in this case proved of great advantage, and, as a contribution to the subject of consanguinity, seems worthy of being put on record. In 1883, the writer, whose previous training had been almost exclusively in the domains of palæontology and the distinctly sedimentary formations, finding himself in a region of crystalline and metamorphic rocks felt the need of acquainting himself with modern petrographic methods. Working in complete isolation without previous instruction in this branch, without material for comparison and almost without literature, he was also without the traditions of the science and preconceived ideas of the relations of the different petrographic groups, and thus free to follow out the lines of investigation suggested by their apparent field relations. In working over the material at hand in the National Museum at Rio, attention was attracted to specimens of nepheline-syenite, or foyaite (using that term as a general title for the holocrystalline nepheline-orthoclase rocks) and as one of the localities, the peak of Tingua, was readily accessible from Rio an attempt to determine its field relations was resolved upon. This heavily wooded mountain proved a hard nut to crack, and several excursions gave very slender results beyond the fact that with the predominant foyaite, phonolite and basaltic rocks, which have since been named monchiquites by Prof. Rosenbusch, occurred. These two last types, found only in loose blocks or in small dykes in gneiss that was clearly older than the foyaite, gave no idea of their relations to the latter rock except that at one point a small dyke of phonolite containing polyhedral inclusions of foyaite, like raisins in a pudding, was observed cutting foyaite of the same type as the inclusions. An examination of a series of railroad cuttings between the peak and the city showed a plexus of phonolite and monchiquite dykes together with a peculiar feldspathic rock of syenitic aspect, which, as they did not extend to the city, were suggestive of a possible genetic connection with the eruptive center of Tingua, or of some other similar center in the vicinity. The occurrence of phonolites, hitherto only known on Brazilian soil on the volcanic island of Fernando de Noronha, suggested a search for phonolitic centers of eruption. About this time a chance collection made by a naval officer from the island of Cabo Frio, 60 miles from Rio, came to hand. As it contained specimens of both phonolite and foyaite, an excursion was resolved upon, guided by the thought that a rocky island on an open coast should give good exposures and thus perhaps prove a better point than Tingua for the study of the problems presented in this mountain. The island, from two to three miles long and from one-fourth to one-half mile wide, was found. to give an almost continuous rock exposure about its entire margin. About four-fifths of the island is composed of coarse grained sodalite-bearing foyaite somewhat different from the Tingua type, and like it cut by numerous dykes of phonolite. The remainder consists of augite-syenite of two types, except a small point which is distinctly tuffaceous and cut by innumerable small dykes of a basaltic character. In one place dyke-like masses and large boulder-like inclusions of a pyroxene-plagioclase rock of a gabbro type occur. The coast of the mainland, distant half a mile more or less from the island, is entirely free from rocks of a syenitic character, and is composed of gneiss cut |