TACONIC SYSTEM. 27 



and frequently auriferous, or cupriferous. The magnetic and specular iron ores 

 also occur with the material of the slates as a deposit of the same age, and consti- 

 tuting part of the same system. This mineral wealth is so distributed it is practi- 

 cally inexhaustible. The Taconic appears in Missouri, Arkansas, and Texas. The 

 iron ore district about Iron Mountain and Pilot Knob containing porphyry rocks 

 is of this age, but the granite to the east is Laurentian. The ore is found in 

 very thick veins in Iron and Shepard Mountain, and Pilot Knob. It is specular 

 ore, containing between sixty and seventy-five per cent of iron, free from sulphur 

 and bearing no more than a mere trace of phosphorus. The rocks appear in 

 numerous places in the Rocky Mountain ranges from Mexico to British Columbia, 

 often exposing great geographical areas and an immense thickness, and they are 

 usually metalliferous. 



§ 50. The genera, regarded as typical of the Taconic fauna, and which do not 

 pass up into Silurian rocks, are Paradoxides, Microdiseus, Atops, Elliptocephala, Cono- 

 eorypJie, Anopolenus, Bathynotus, Solenopleura, Acrothele, Salterella, Scenella, Jphidea, Hyo- 

 lithellus, Archceocyathns, and Ethmophyllum. There are some others peculiar to these 

 rocks, but they are either obscure or limited in their distribution. Some genera 

 closed their existence in Silurian time, others reached the Devonian age, and some 

 from this remote period, as Orthis, Orthisina, Orthoceras, and Leperditia, continued 

 to live to the Carboniferous, though Orthoceras reached its most remarkable de- 

 velopment in the Black River Group, and Orthis in the Hudson River. Not a 

 single species belonging to the Upper Taconic system crossed over the line that 

 separates it from the Potsdam Group of the Lower Silurian, so far as any reliable 

 determination has thus far been made. This, supported as it is by a want of con- 

 formability, indicates a vast lapse of time between the deposit of the Upper Taconic 

 and the commencement of the Potsdam period. The Taconic is composed in part 

 of the disintegrated materials of prior Laurentian rocks, while the Potsdam repre- 

 sents the washings of the Laurentian and Taconic. The order Graptolida appeared 

 in this system, and reached its maximum development of genera, species, and num- 

 bers (if the Point Levis beds referred by the Canadian Geologists to the Quebec 

 Group belong to the Upper Taconic, as claimed by Marcou and others, and as the 

 author believes), and became extinct in the Upper Silurian System. This is the 

 first order of animal life to reach the highest stage of its existence, and the first to 

 become extinct. It is referred to the class Hydrozoa, but if more was known of it, 

 very likely it would form a distinct class. 



§ 51. The Cupriferous series of the lake region, called also the Keweenaw, 

 Keweenian, Keweenawan, and Nipigon series, is supposed to underlie nearly the 

 whole basin of Lake Superior, or an area of about 28,000 square miles, and a sur- 

 face area upon the borders of the lakes and their immediate vicinity of about 

 18,000 square miles. This series has been divided into an upper and lower division, 

 with an estimated maximum thickness of 15,000 feet for the upper division, and 35,000 

 feet for the lower, which rests upon the slates and quartzites of the Taconic System, 

 the last having a variable thickness that reaches a maximum of at least 22,000 

 feet. The Cupriferous series consists of eruptive flows and detrital rocks, with mas- 

 sive dykes. The region was, in Taconic days, represented by a volcano, which has 

 sunk beneath the waters of the lake. The flows were followed by detrital rocks, 

 representing the intervals of time between them ; but these detrital rocks are com- 



