STRAND-LINE DISPLACEMENTS 489 



ward, along a series of Taconic geosynclines that ended in the making of 

 a series of Taconic ranges." With the exception of the Appalachian rev- 

 olution which closes the Paleozoic, this secular disturbance was the most 

 marked one of the era, withdrawing as it did the water from the North 

 American continent to such an extent that finally all retreated except that 

 in the immediate Mississippi valley. Here several pulsations of the sea 

 have left a record of small faunas. In the outer portions of the Saint 

 Lawrence trough, however, the attracted sea continued throughout the 

 time of the Taconic revolution, and on the island Anticosti there is a good 

 fossiliferons record of this entire interval preserved in over 1,700 feet of 

 thin-bedded limestones and shales. This record begins early in the Eich- 

 mond, and continues unbroken into the Eochester of the Siluric, the entire 

 section having a thickness of more than 2,300 feet. In the entire depth 

 of these deposits there are but two thick shale zones, one in the Upper 

 Eichmond, the other just before Clinton time. That this shallow bay felt 

 the unrest of the closing stages of the "Ordovicic" is proved by the sec- 

 tions described by Eichardson. 12 * Throughout Divisions A and B, which 

 have a combined thickness of 959 feet, are innumerable zones of intra- 

 formational conglomerates. This is the time of the Eichmond of the 

 Mississippian sea. The fauna of the Eichmond then continues through 

 Division C, having a thickness of 306 feet, where more conglomerates 

 were seen. Division D represents about the time of the Ohio Clinton of 

 the Siluric, when the Magaran invasion takes on a more decided aspect. 



Siluric period or system — Magaran transgression (see maps, plates 

 63-68). — The Taconic revolution ended in an almost complete emergence 

 of the North American continent ; in fact, the continent was at that time 

 nearly as large as at the close of the Proterozoic. The only area remain- 

 ing submerged was the outer portion of the Saint Lawrence sea, this being 

 represented by a bay, an attracted arm of the ocean, extending from 

 southwest of Anticosti across northern Newfoundland. In the imme- 

 diate region of the Mississippi river, as far north as northern Illinois, the 

 sea appears to have been erratic, and the record is not only incomplete 

 but the deposits are very thin, the best representation being in the Edge- 

 wood beds. This horizon is also thought to indicate the time of the top- 

 most Medina, the zone with the marine fauna described by Hall in 1852. 

 The Medina deposits are of a synclinal sea occupying restricted areas of 

 the Appalachian sea. These were followed by the beginnings of the 

 Magaran transgression first seen in the Ohio-Clinton deposits. In the 

 later Clinton the more widespread inundation was continued, and attained 



124 Richardson : Report of Progress, Geological Survey of Canada, 1S57, pp. 191- 



