HYPOGEIC WORK. 393 



America best exhibits typical continental growth, because it stands by 

 itself between the two oceans, free from other lands on the east, south, 

 and west. In this it is greatly in contrast with Europe and Asia. In all 

 its structure it shows that its orographic courses were outlined at its incep- 

 tion, and that its features were gradually developed from age to age, in 

 accordance with the foreshadowed system. The Archaean protaxes have 

 almost the lengths of the adjacent continental borders, and the systems of 

 ranges of later elevation, on the Atlantic and Pacific sides, have parallel 

 courses and like extent. They are not irregularly distributed groups or 

 knots of mountains, but elevated lines in the continental structure, orderly 

 placed according to principles and forces that were already at work in 

 Archaean time. 



Eock-making went forward under like comprehensive methods with the 

 mountain-making. AVhen Archaean time closed, North America comprised a 

 great Interior Continental or Mediterranean Sea, partially separated by the 

 protaxes from the continental-border seas on the Atlantic and Pacific ; and, 

 besides, there were, in some parts of the borders, parallel troughs or basins 

 between Archaean confines. Through the following ages, these seas were 

 doing their various work in rock-making, bringing first to a finish, and 

 emergence with orographic aid, the eastern half of the continent ; and then 

 giving a like degree of progress and emergence to the western half; and, 

 finally, under a comprehensive agency, carrying the whole area, from east to 

 west, to completion. 



5. The earth an individual in development. — The system of feature-lines, 

 displayed in the islands of the Pacific, is virtually that of a hemisphere, for 

 nearly half of the equator lies between the ocean's eastern and western 

 limits. It may be rightly taken, therefore, as the system of the globe. All 

 north-and-south lines are subordinate lines in this system. There is no 

 network of pentagonal lines of dislocation (De Beaumont), or of tetrahedral 

 lines (William L. Green, 1857-1887), or of dodecahedral lines, as urged by 

 R. Owen, of Indiana, in his later paper on the earth's features (1888); for 

 the existence of continental regions and oceanic basins implies local differences 

 in the nature of the material over the sphere, when surface cooling began, 

 that made such lines of symmetry impossible. Instead, the actual physiog- 

 nomy includes long parallel ranges of lines, often bending in great curves, 

 with transverse lines nearly at right angles, and a reference in all to the 

 positions and forms of the continental and oceanic areas. The island chains 

 of the Pacific, 1000 to 5000 miles long, are separated by underwater valleys, 

 reaching in some cases to depths of 28,000 feet, or over 40,000 below the 

 highest island summits. The system of feature-lines of the oceans is 

 exhibited also by the continents, but with irregularities incident to the 

 forms, positions, and consequent resistances of the nucleal land-masses. 



System through regular progress is abundantly proved, but the special 

 causes determining the details of the system are not yet all understood. 

 The following are some of the points awaiting explanation : — 



