ISO DE. THOMAS STEERY HUNT ON THE 



Transition by Maclure, includes the Primitive Quartz-rock, the Primitive Lime-rock, and the 

 Transition Argillite of Eaton, and is the Lower Taconic of Emmons, and the Itacolumitic 

 group of Lieber. This series, which I have preferred to call Tacouiau, is essentially one of 

 Transition crystalline rocks. The quartzites, which predominate in the lower portion, 

 contain much detrital matter, and are sometimes conglomerates. They are, however, 

 often vitreous or granular, the latter variety being sometimes flexible and elastic, and 

 constituting what is called elastic sandstone or itacolumite. These quartzites, like the 

 limestones of the series, often contain an indigenous micaceous substance, which is in 

 most cases a hydrous muscovitic mica, related to sericite or to damourite. A similar min- 

 eral predominates in certain layers of soft unctuous lustrous schists, which, from their 

 aspect, have been called talcoid or naagnesian, and are found intercalated alike with the 

 quartzites and the limestones of the series. The latter, often more or less magnesian, are 

 generally finely granular, and yield marbles for statuary and for architecture. They are 

 often variegated in color or banded with green or gray, constituting cipolins. The min- 

 eralogy of the limestones and their associated crystalline schists, has been noticed in 

 §§ 51, 65, 68, *76, *79, and it has been shown that the Taeouian is an important ore-bearing hor- 

 izon, including, besides great deposits of magnetite, others of siderite and of pyrite. Both 

 of the latter species, by epigenesis, give rise to hydrous iron ores, which, throughout the 

 Appalachian region, characterize the outcrops of the series, and are generally imbedded 

 in clays, the result of the subaerial decay of the enclosing schists, which, it may thence 

 be conjectured, include, in many cases, large proportions of a feldspathic mineral. The 

 aro"illites of the Taconian, often yielding roofing-slates, are interstratified with more or less 

 silicious beds, and occur chiefly in the upper part of the series. The mineralogy of the 

 Taconian has been further discussed in the author's essay on " The Origin of Crystalline 

 Rocks " in the Transactions of the Royal Society of Canada, Vol. IL Sec. Ill, p. 63. 



§ 19*7. These Taconian rocks are not confined to tlie Appalachian valley. Extending 

 southward therefrom, they are traced in Pennsylvania along the eastern base of the 

 Blue Ridge into North Carolina, and are found in outliers to the east over the Atlan- 

 tic belt from Georgia to New Brunswick. To the west of the great valley, they are 

 known to underlie the eastern part of the paleozoic basin, and appear in eroded anticlinals 

 from beneath the coal-measures, alike in Alabama and Pennsyh^ania, where they are 

 directly overlaid by Ordovician strata. They are seen in similar conditions, lying un- 

 conformably beneath the Ordovician limestones of the Ottawa basin, in Hastings County, 

 Ontario, and are believed to be represented by the great series of argillites, quartz- 

 ites and limestones around Lake Superior, which, in 1873, I called the Animikie series, 

 and which there underlie, iinconformably, not only the Cambrian (Potsdam) of the Mis- 

 sissippi area, but, according to Irving, the Keweeniau series also. The presence of Lower 

 Taconic rocks was long since asserted by Houghton in the northern peninsula of Michi- 

 gan, and it is probable that a part of what has since been called Huronian belongs to this 

 Animikie or Taconian series (§ 89, 90). The argillites and c^uartzites which, in the Black 

 Hills of Dacotah, intervene between the older crystalline rocks and the Cambrian, resem- 

 ble those of the Taconian. 



§ 198. The Taconian series is not destitute of evidences of organic life, but contains, 

 in the granular quartzites near its base, the typical Scolithus linearis at many points through- 

 out the Appalachian valley. Similar markings in the silicious beds of the series in Hast- 



