2 BULLETIN OF THE LABORATORIES 



know, great accumulations result in areas of elevation, while vice-versa, 

 lesser deposits might be held as forming the lowest depths. James 

 D. Dana has attributed the zigzag arrangement of continents to tor- 

 sion with the maximum torsion represented by a belt of volcanoes, 

 and the earth's feature-lines as consequences in part of the pressure or 

 tension attending torsion. 



In our own country it can be readily shown that the North Amer- 

 ican continent had attained the outlines of its present form at the close 

 of the Archaean age, subsequently developing southward into tlie 

 Appalachian axis ; that westward from there the surface deposits 

 prove that it was coexistent with Carboniferous time, while west of a 

 line drawn from the eastern longitude of Dakota the great Mesozoic 

 and Tertiary deposits took place, the great climax of physical activ- 

 ity resulting in the evolution of the Mesozoic age, together with lesser 

 resultant actions at the close of the Tertiary, or during a period very 

 nearly contemporaneous with the Glacial epoch. Coexistent with 

 this, it should also be observed that deposition took place from the 

 north to the south, leaving the southern states adjacent to the Atlan- 

 tic, Gulf of Mexico, and the Rio Grande of Tertiary and other later 

 formations. We have attempted to show in a very general way the 

 course of development among the sedimentary rocks, and it is thought, 

 that as the general development has been westward, so we may be able 

 to indicate the origin more exactly of portions of the Palaeozoic strata 

 from sources eastward of their main deposition. 



Any consideration of the origin of the later fragmentary rocks, 

 involves not only an account of the adjacent land areas, but also the 

 agencies by which they might be removed. The argument of Mr. 

 Bull that the denuding action of tides must have been much greater 

 among the rocks under discussion, cannot ai)parently find any very 

 strong substantiation in nature, either from an organic or physical ba- 

 sis. Mr. Bull supposes that on account of the greater proximity of 

 the moon at this time, that the action of tides would be greatly in- 

 creased, causing material to be eroded and deposited in a manner al- 

 most inconceivable at the present. There are three objections to this 

 theory : Primarily, that the nebular hypothesis of Laplace involves the 

 fundamental idea that heat is evolved as a result of contraction, not 

 taking into account that the intense heat of the sun would be more 

 apt to cause an expansion instead of contraction along its diameter, 

 according to all the known laws of Physics, while this involves indi- 



