W. H. Twenhofel — Physiography of Newfoundland. 19 



are considered evidence of the present dissection, but one 

 time perfection of a peneplain, a plain of erosion of remark- 

 able perfection extending over the whole of Newfoundland.* 

 If the valleys were tilled to the level of the average mountain 

 summits the resulting plain would be strikingly perfect, would 

 be 2000 feet high on its western border and pass beneath the 

 sea on its eastern with an elevation of about 700 feet at the 

 shore. This slope probably represents the tilting that has 

 occurred with uplift, which, however, does not appear to have 

 been a simple warping uplift, but by different blocks acting as 

 units, of which the Long Range is perhaps the most conspicu- 

 ous. On this ancient plain the rivers were free to wander 

 where they would, structure and texture of rock being mini- 

 mized as factors of stream control. They probably crossed 

 the site of the present mountain ranges and, when the land 

 arose, each stream struggled to maintain its position. The 

 Humber alone carved its way through the rising Long Range 

 blocks and by developing northern and southern tributaries 

 took from other western streams their sources, but thus pre- 

 served their waters for the western sea. 



Attempts to fix the time of the close of the cycle of erosion in 

 which this peneplain was carved meet with difficulty. The 

 latest rocks involved in the folding that probably initiated the 

 erosion cycle are of Pennsylvania!! age and the upper wide and 

 flat-floored valleys are pre-glacial. 



In the eastern United States throughout the Appalachians, 

 the existence of an extensive peneplain, completed before the 

 end of Cretaceous time, is now universally admitted and with 

 this base level that of Newfoundland is tentatively correlated, 

 and the period of development and close of the cycle assumed 

 to be the same. 



Elevated valleys. — These valleys, situated at altitudes of 

 from 800 to 1200 feet, were probably carved during a period 

 of temporary stability when the land was lower by an amount 

 almost equal to their present elevation. The evidences of an 

 older topography at this level are so evident that any possi- 

 bility of ascribing them wholly to the work of ice is eliminated 

 and to the work of this agent can merely be assigned their 

 U-shape and greater width. Except that they are pre-glacial 

 their time of origin cannot at present be determined in New- 

 foundland, but the observations of numerous workers in many 

 parts of the Appalachians have proven the development of a 

 partial peneplain during Tertiary time and these elevated val- 

 leys were perhaps a part of that level. There are not sufficient 



* Without discussion the writer assumes that this plain owes its origin to 

 subaerial erosion and not marine, considering that the numerous conical 

 residuals and the extensive area support the assumption. 



