472 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



"Thus the enlargement went on to the southward, each period making some 

 addition to the main land, as each year gives a layer of wood to the tree. Not 

 that this addition was free from oscillations, causing submergences, for these 

 continued long to occur; but the gain, on the whole, was a gain" (343, 344). 



"The Azoic nucleus of North America, spreading southward, formed a penin- 

 sula in Northern New York [Adirondackia]. Even this bend in the nucleus 

 continues in the finished continent, for New England has the same outline. Its 

 east and south coast-lines are but a repetition of the east and south coast-lines 

 of the old Azoic peninsula. This exact copying of the nucleus by the growing 

 continent proves, better than all other evidence, the grand fact that the prog- 

 ress has been through oscillating forces acting against the stable Azoic nu- 

 cleus, and also that the system of evolution has been under profound law" 

 (Dana. Manual of Geology, 1863, 737). 



Laurentia was the most persistent positive element of North Amer- 

 ica, large portions of it having been land continuously, and around its 

 xerotic, western, and southern sides were deposited Paleozoic or Meso- 

 zoic sediments. In the west and south great parts were inundated in 

 Ordovicic and Siluric times. "With the Devonic the "shield" became decid- 

 edly larger, and increased still more extensively in the Mississippic. The 

 Hudson bay depression was of very early origin, appearing for the first 

 time in the middle Ordovicic, when it was a far larger continental sea 

 than at present. From the close of the Siluric until late Tertiary times 

 no marine waters appear to have invaded this region, and from the begin- 

 ning of the Paleozoic it seems to have been devoid of volcanic activity. 

 The southern portion of Davis strait also gives evidence of being of very 

 ancient origin, for the Ordovicic sea must have extended across southern 

 Baffin Land, thus connecting the northern Atlantic with the interior Hud- 

 son sea. Early in the Siluric, Ungava appears to have united with Baffin 

 Land, establishing a land barrier against further Atlantic overlaps until 

 modern times. 



Laurentia was the western end of the Great North Land of the Paleozoic 

 and Mesozoic, sometimes erroneously called Atlantis. Nearly all geolo- 

 gists and zoogeographers are agreed that it extended across Greenland, 

 Iceland, Norway, and united with the "Baltic shield," best seen in 

 Finland. 



Laurentia is readily divided into seven subelements that at times are 

 separated from one another by shallow sea-ways, but are all comprised in 

 one continuous land-mass subsequent to the Siluric. These subelements 

 are as follows : Greenlandia, which embraced present Greenland, was from 

 the close of the Siluric until late Cretacic times united with Frariklinia, 

 when Davis strait was extended to Disco and Nugsuak. Along its north- 

 eastern shores are Paleozoic and Mesozoic strata, showing that the Arctic 

 ocean here lapped the Great North Land. Southeastern Greenlandia is 



