670 



TACONIC SYSTEM. 



T 



TACONIO SYSTEM. The most interesting 

 subject of discussion among American geolo- 

 gists, shared in to some extent by those of Eu- 

 rope, is the question of the recognition of the 

 "Taconic System" of Dr. E. Emruons. This 

 division of stratified rocks underlying the lower 

 silurian was proposed by him in 1842, in his final 

 report on the geology of that portion of New 

 York of which he had charge ; and in 1844 

 he published a work expressly devoted to this 

 subject, entitled " The Taconic System." The 

 same arrangement was originally proposed by 

 Professor Eaton, the geologist ; and Dr. Em- 

 raons, in adopting it, subdivided the group as 

 follows, commencing with the lowest mem- 

 ber : 1. Granular Quartz ; 2. Stockbridge Lime- 

 stone ; 3. Magnesian Slates ; 4. Sparry Lime- 

 stone ; 5. Roofing Slates ; 6. Silicious Conglom- 

 erates ; 7. Taconio Slates ; 8. Black Slates. 

 He traced the series along the eastern border of 

 New York, from the southern extremity of the 

 State through western Massachusetts and cen- 

 tral Vermont into Canada, and named it from 

 the range of mountains containing these strata, 

 which runs nearly north and south near the 

 eastern boundary line of New York. He and 

 other geologists afterwards recognized the same 

 group as extending the whole length of the Ap- 

 palachian chain, and attaining a thickness of 

 some 30,000 feet. ' Its metamorphic character, the 

 uplifted and even supposed overturned position 

 of the strata, and the obscurity of the few fos- 

 sils they contained, had always rendered it ex- 

 tremely difficult to deterimne its true relations 

 to the adjacent. "What Dr. Emmons regarded as 

 its upper members seemed indeed to pass under 

 the gneiss of the Green Mountains, which Dr. E. 

 regarded as a primitive azoic rock ; and this could 

 be explained only on the supposition of a grand 

 overthrow of the whole belt of palaeozoic rocks. 

 The fossils observed were a few graptolites in 

 the black slates, and in some of the other strata 

 fucoides, what appeared to be trails of an- 

 nelides, and two trilobites, which Dr. E. de- 

 signated Atops trilineatus and Elliptocephala 

 asaphoides, and believed to be characteristic of 

 the system, and of especial interest as the oldest 

 representatives of animal life. His views were 

 opposed from the first by most of the American 

 geologists. The Professors Rogers of Pennsyl- 

 vania and Virginia found, as they believed, a 

 gradual passage of the sandstones, shales, and 

 limestones of the lower silurian, into these 

 obscure groups on leaving their more western 

 and comparatively little disturbed outci-ops, 

 and approaching the highly metamorphic dis- 

 tricts on the eastern side of the Appalachian 

 chain, thus proving the two to be of the same 

 age ; and Professor Hall, of the New York sur- 

 vey, regarded the trilobites of Dr. Emmons, 

 the first named, as identical with the Trianthrus 

 Beckii, the characteristic trilobite of the Utica 



slate, and referred the other to the genus Ole- 

 nus, another species of which was known in the 

 Hudson River slates, and in no lower rocks. 

 Thus both on stratigraphical and pakeontolog- 

 ical grounds the most eminent geologists of 

 the country classed these disputed strata with 

 the lower silurian, and the Taconic system 

 was naturally treated with neglect. In Can- 

 ada the same group has been traced by the 

 Canadian geologists, from the northern extrem- 

 ity of Vermont to the neighborhood of Que- 

 bec, and thence along the south side of the St. 

 Lawrence to the mouth of that river, at Cape 

 Gasp6 ; and has everywhere been referred to 

 the Hudson River group of the New York sur- 

 vey, or the upper members of the lower silu- 

 rian. It is not a little remarkable, that after 

 this question had been considered settled by 

 most geologists for as many as 10 or 15 years, 

 it should have been brought up again by a geol- 

 ogist in Austria, M. Joachim Barrande, who 

 recognized in the description, by Professor 

 Hall, of three trilobites found in the uppermost 

 slates of the Hudson River group, near the 

 town of Georgia, Vermont, and named by him 

 Olenus Thompsoni, O. Vermontana, and Peltura 

 (Olenus) holopyga, the characters of the trilo- 

 bites of the primordial fauna of Europe, a new 

 group of fossils established by him, of an older 

 date than those of silurian age. Hence, on the 

 gi'ound that each geological epoch has its prop- 

 er and characteristic forms, which once extinct 

 reappear no more, he questions whether these 

 fossils are not from a formation older than the 

 Potsdam sandstone, and that this is the " Ta- 

 conic group " of Dr. Emmons. 



The discovery, in 1860, of a great number of 

 mollusca, articulata, graptolidas, and radiata in 

 the calcareous strata of the Quebec group, 

 found near Quebec, Canada, a formation con- 

 sidered of the same age with the slates of 

 Georgia, Vermont, furnished full evidence of 

 this group being at least as ancient as the Pots- 

 dam sandstone, and perhaps belonging to the 

 primordial zone of Barrande. Professor Hall, 

 however, while admitting that these rocks on 

 palfeontological evidence are of greater age than 

 had been before admitted, still hesitates to ad- 

 mit that the occurrence of a small number of 

 established primordial types should be sufficient 

 authority for bringing into this zone a large 

 number of genera associated with them, and 

 heretofore regarded as beginning their existence 

 in the second stage, or succeeding fauna ; and 

 consequently does not recognize the lower por- 

 tion of the rocks of the Quebec group as consti- 

 tuting a part of the Taconic system. 



Other evidence of the occurrence of the 

 primordial zone in the United States is afforded 

 by the discovery of the trilobite Paradoxides 

 Harlani, in the metamorphic slates at Braintree, 

 Mass., announced by Professsor W. B. Rogers 



