Shaler.] 130 [October 7, 



the perplexing facts of alternation of elevation and subsidence to 

 reconcile with this uniformity in other regards, and no hypothesis 

 which fails to account for this extreme variability in the character 

 of the movement with the equability of the action over wide areas, 

 will be entitled to consideration. 



Our evidence shows us sea hnes of thousands of miles in length, 

 which have, during the present period, been imdergoing a tolerably 

 uniform upward movement. Are we to suppose that the extension of 

 this movement on lin^s at right angles to the shore has been as great, 

 or are we rather to suppose that the action of elevation acted along 

 one line, and that this line, for some reason or other, has coincided 

 with the shore? This question leads us to search for the nature of 

 the cause of these shore oscillations of level. 



If we assume that the great folds of the earth's crust, termed con- 

 tinents, are the result of the accommodation of the outer envelope to 

 a diminished interior, then it follows that in such movement the sea 

 furrows would be steadily lowered, and the continental folds corre- 

 spondingly elevated above the shore line as contraction went on. 

 The author has elsewhere briefly stated some reasons for believing 

 that through the deposition of sedimentary matter, and the conse- 

 quent rising in the isogeotherms in the strata beneath, the ocean floors 

 would always bend downward, and the land areas bend upward, as the 

 shi-inking of the interior of the earth went on. Be this as it may; 

 the result of the sinking of the ocean bottom and the elevation of the 

 land, would necessarily be the movement of the segment of the cnist 

 from the centre of the continents to the centre of the sea, with the 

 axis of rotation or fulcrum point, near the shore hne. If the conti- 

 nents and sea basins owe their origin to wrinkling of the crust, this 

 conclusion seems to be necessary. Admitting such a rotation about a 

 line near the shore, then it follows that one of three conditions may 

 prevail. It is possible that the point of rotation may be precisely at 

 the shore, to the seaward of the shore, or some distance from the 

 water on the surface of the land. It will be easily seen from inspect- 

 ing the accompanying diagram, (Fig. 1,) that in the former case, very 

 extensive actions of subsidence and elevation might take place with- 

 out affecting the position of the shore line in the least, unless in the 

 changes of level the holding capacity of the sea basin was greatly 

 modified ; any such effect would necessarily be very slight, as it would 

 be equalized by the waters of all the oceans. In the third condition 

 (Fig. 1), that where the pivot point was to the landward of the shore, 

 there could be no other result than the apparent sinking of the shore, 



