September 12. 1884.] 



SCIENCE. 



239 



They are wanting or comparatively rare throughout 

 the rest of the crystalline rocks. 3°. The next lower 

 grand division might be styled the ' black mica slate 

 group/ This group contains much carbon, causing 

 it to take the form of graphitic schists, in which the 

 carbon sometimes amounts to over forty per cent. 

 These schists are frequently quartzose and also fer- 

 ruginous. Associated with these hlack mica slates, 

 which often appear also as dark clay-slates, are actin- 

 olitic schists ; the whole being, in some places, inter- 

 stratified with diorite. 4°. Underneath this is a 

 very thick series of obscure hydro-micaceous and 

 greenish magnesian schists, in which, along with 

 gray quartzite and clay slates, occur the most im- 

 portant deposits of hematitic iron-ore. This division 

 of the crystalline rocks has numerous heavy beds of 

 diorite. 5°. Below this series of soft schists is the 

 great quartzite and marble group. The marble lies 

 above the quartzite, and in the Menominee region 

 has a minimum thickness of at least a thousand feet. 

 This is a most persistent and well-marked horizon. 

 In northern Minnesota, the great slate-conglomerate 

 of Ogishke Muncie Lake, with a thickness exceed- 

 ing six thousand feet, seems to represent the lower 

 portion of the great quartzite of this group, and to 

 he the equivalent of the lower slate-conglomerate of 

 the . ' typical Huronian ' in Canada. 



Now, the difficulties of the situation arise when we 

 cast about to find names for these parts. What are 

 the eastern representatives of these western groups, 

 and by what designations shall they be known? 



We meet, at the outset, with the question, Is there 

 a formation such as claimed by Emmons, — the Ta- 

 conic ? On this geologists are yet divided. Having 

 given the subject very careful consideration, Professor 

 Winchell was ready to state his very positive convic- 

 tion that Dr. Emmons was essentially right, and that 

 the Taconic group will have to be recognized by 

 geologists, and adopted in the literature of American 

 geology. 



In the first presentation of the Taconic system, Dr. 

 Emmons extended it geographically too far east, and 

 unfortunately chose a' name for it which is appropri- 

 ate only to a part of that eastward extension. Dr. 

 Emmons's claim, however, in all its essential points, 

 remains intact. This consists in the existence of a 

 series of sedimentary deposits, largely metamorphic, 

 below the Potsdam sandstone, and separating the 

 Potsdam from the crystalline rocks known as 'pri- 

 mary ' in an orderly chronological scheme. It is not 

 necessary to refer to the controversies that arose from 

 the creation of the imaginary Quebec group, nor to 

 characterize in deserved terms the attempt to bury 

 the Taconic in the Quebec coffin. 



There may be reasons why the current literature 

 of American geology is almost silent respecting the 

 great work of Emmons, and why the Taconic is not 

 known among the recognized geological formations. 

 But we have nothing to do with these at this time. 

 We have now only to say, that it seems necessary to 

 admit, that when Dr. Emmons insisted on a great 

 group of strata belonging to the age of the lower 

 Cambrian, lying below the Potsdam sand-rock in 



New York, he had some foundation more substantial 

 than imagination or mere hypothesis. 



If we examine the descriptions given by Dr. Em- 

 mons of his Taconic system, we shall find that he 

 makes the following broad stratigraphic distinctions: 

 1°. His highest member is what he designates 'black 

 slate,' which he declares, in some cases plunges ap- 

 parently beneath the ' ancient gneiss,' and contains a 

 considerable amount of carbonaceous matter. 2°. 

 Under the black slate his next grand distinction was 

 the so-called Taconic slate, which he described as 

 argillaceous, siliceous, and 'talcose;' thickness about 

 two thousand feet. 3°. Below the great mass of soft 

 schists, he described a mass of five hundred feet of 

 limestone, designated ' Stockbridge limestone,' which 

 graduates downward into ' talcose ' or magnesian 

 sandstones and slates ; the whole having a thickness 

 of about seventeen hundred feet. 4°. Under this 

 limestone is his ' granular quartz ' rock, more or less 

 interstratified with slates, and becoming, in some 

 places, an immense conglomerate with a 'chloritic 

 paste.' 5°. The 'ancient gneiss,' on which the Ta- 

 conic system was said to lie unconformably. 



Now, it requires but a glance to perceive how clearly 

 this order coincides with that which has been inde- 

 pendently and laboriously worked out in the north- 

 west. We have in both instances a ' black slate,' and 

 below this in both cases is an immense series of soft 

 hydro-mica and magnesian schists. These, again, are 

 followed by crystalline limestone, or marble, which 

 changes downwards to slate, and a hard sand-rock. 

 Below this is the great bed of quartzite; which is, at 

 the base, coarsely conglomeritic with masses of rock 

 from the great underlying series of gneiss. 



We are now, however, confronted with another dif- 

 ficulty. The geologists of Michigan and Wisconsin 

 have set aside Dr. Emmons's identification of the 

 Menominee rocks with the Taconic, in 1846, and have 

 called them Huronian. It becomes necessary, there- 

 fore, to ascertain of what the Huronian system con- 

 sists. 



The 18,000 feet of the Huronian system on the 

 shores of Lake Huron include 900 feet of limestone. 

 2,000 feet of ' chloritic and epidotic slates,' and 15,100 

 feet of quartzite and conglomerate. Perhaps 5.000 

 feet of this thickness may be considered intrusial. 

 This will leave 12,000 feet, at least, for the aggregate 

 thickness of quartzite and conglomerate, being 

 nearly double that observed in the same horizon in 

 northern Minnesota. It is plain to see, that, if there 

 be any parallelism between these beds and the various 

 groups made out in the north-west, the whole of 

 these strata must be made the equivalent of group 5. 

 or the quartzite and marble group. 



There is, therefore, a conflict between the Taconic 

 and the Huronian, both in respect to the horizon 

 which they are intended to cover, and in the hori- 

 zon of rocks which they actually compass. The Hu- 

 ronian, however, in its original and typical descrip- 

 tion, can be parallelized with only the very lowest of 

 the strata that were included in the typical and origi- 

 nal Taconic; while the Taconic stretches upward at 

 least as far as to include the fourth and third grand 



