Handbook of Paleontology 255 



many places lies unco.nformably upon the Middle Ordo- 

 vician, indicating a period of uplift and erosion. Older 

 Ordovician rocks fringe the great northern Precam- 

 brian area in the west and are even found in the islands 

 of the Arctic sea. 



The oscillatory movements, that is, the submergences 

 and emergences, throughout the Ordovician were slow 

 and gentle, so that the Ordovician period may be regarded 

 as a period of quiet, with epicontinental seas gradually 

 increasing in size to their greatest expansion in the middle 

 epoch when the greater part of the southeastern quarter 

 of the continent was submerged. At the end of the period 

 the lands were again drained leaving the outlines of the 

 continent much as they are today. The close of the Ordo- 

 vician is marked by a time of widespread disturbance and 

 mountain making, known as the Taconic Emergence, Dis- 

 turbance, or Deformation, traces of which are found in 

 North America and Europe, especially along the Atlantic 

 slope of each continent. The great masses of sediments 

 that had accumulated in the northern part of the Appa- 

 lachian trough were subjected to lateral pressure and 

 folded. The Taconic range along the line between New 

 York and New England was upheaved at this time and 

 has given its name to the period of deformation. Its 

 rocks were greatly compressed, folded and metamor- 

 phosed and sedimentary beds from the Cambrian to and 

 including the Ordovician were involved. Evidences of 

 this disturbance have been found as far south as Ala- 

 bama. In Nova Scotia and New Brunswick Silurian 

 beds are found resting upon the upturned edges of Ordo- 

 vician strata but the upheaval does not appear to have 

 extended to the northern part of the Gulf of St Law- 

 rence. In the Hudson valley of New York and in parts 



