the Earth's Contraction from Cooling. 49 



consists, like the Rocky and other mountain-chains, of several 

 monogenetic ranges, the more important of which are: — (1) 

 The Highland range (including the Blue Ridge or parts of it, 

 and the Adirondacks also, if these belong to the same process of 

 making) prse-Silurian in formation. (2) The Green -Mountain 

 range, in western New England and eastern New York, com- 

 pleted essentially after the Lower Silurian era or during its 

 closing period. (3) The Alleghany range, extending from 

 southern New York southwestward to Alabama, and completed 

 immediately after the Carboniferous age. 



The making of the Alleghany range was carried forward at 

 first through a long-continued subsidence — a geo synclinal* (not 

 a true synclinal, since the rocks of the bending crust may have 

 had in them many true or simple synclinals as well as anticli- 

 nals), and a consequent accumulation of sediments which occu- 

 pied the whole of Palaeozoic time j and it was completed finally 

 in great breakings, faultings, and foldings or plications of the 

 strata along with other results of disturbance. The folds are 

 in several parallel lines, and rise in succession along the chain, 

 one and another dying out after a course each of 10 to 150 

 miles ; and some of them, if the position of the parts which 

 remain after long denudation be taken as evidence, must have 

 had, it has been stated, an altitude of many thousand feet ; 

 and there were also faultings of 8000 to 10,000 feet, or, accord- 

 ing to Lesley, of 20^000 feetf. This is one example of a mono- 

 genetic range. 



The Green Mountains are another example, in which the his- 

 tory was of the same kind : — first, a slow subsidence or geosyn- 

 clinal, carried forward in this case during the Lower Silurian era 

 or the larger part of it, and, accompanying it, the deposition of 

 sediments to a thickness equal to the depth of the subsidence ; 

 finally, as a result of the subsidence and as the climax in the 

 effects of the pressure producing it, an epoch of plication, crush- 

 ing, &c. between the sides of the trough. 



In the Alleghany range the effects of heat were mostly con- 

 fined to solidification, the reddening of such sandstones and 

 shaly sandstones as contained a little iron in some form J, the 



* From the Greek yrj earth, and synclinal, it being a bend in the earth's 

 crust. 



t See an admirable paper on these mountains by Professors W. B. and 

 H. D. Rogers in the Trans. Assoc. Amer. Geol. and Nat. 1840-42. J. P. 

 Lesley gives other facts in his * Manual of Coal and its Topography,' and 

 in many memoirs in the * Proceedings of the American Philosophical 

 Society.' A brief account is contained in the author's ' Manual of Geology.' 



X Oxide of iron produced by a wet process at a temperature even as low 

 as 212° F. is the red oxide, Fe 2 O 3 , or at least has a red powder. (Am. 

 Journ. Sci. 2nd ser. vol. xliv. p. 292.) 



Phil. Mag. S. 4. Vol. 46. No. 303. July 1873. E 



