1GS Mr.'S. V. Wood on the Form and Distribution of the 



northwards along the eastern side of the Rocky Mountains to 

 the Polar Sea ; the Alleghany region forming a great peninsula 

 pointing southwards, and joined to a continental tract occupied 

 by what is now the palaeozoic region of the northern and north- 

 western states of America and of Canada, and the crystalline 

 region of the Hudson Bay territories, but separated from the 

 Rocky-Mountain region by this secondary sea. Here, again, the 

 same changes of level during the secondary period which the At- 

 lantic flank of the Appalachian region presents seem repeated, 

 the newer secondary (cretaceous) formations so overlapping the 

 middle and older secondary that they are mostly found reposing 

 here on the palaeozoic, — the middle and older secondary forma- 

 tions being either absent or so far obscured that, in the present 

 state of their knowledge of this region, the American geologists 

 are at issue whether any formations really referable to the middle 

 and older secondary periods have yet been found west of the 

 Alleghanies*. 



The extensive region of the Rocky Mountains, which includes 

 within it the whole elevated tract between the Mississippi and 

 Saskatchewan valleys on the east, and the Pacific on the west, 

 was until recently almost an unknown region ; but the report of 

 Dr. Hector f, who, under Palliser's expedition, made a rapid 

 survey of part of this chain, shows that, like the Alleghanies, 

 the core of the chain consists of mural precipices of highly in- 

 clined palaeozoic formations, flanked with secondary deposits 

 lying quite unconformably on them, and stretching away from 

 the chain with a very easy dip, the development of the cretaceous 

 formation being such as apparently to have filled the whole val- 

 ley lying between the Rocky Mountains on the west, and the 

 palaeozoic system of the United States and Canada, and the hy- 

 persthene system of the Lake and Hudson's Bay region on the 

 east, from the coast of Texas on the south, to the Polar Sea on 

 the north. Here again, therefore, is exhibited a yet more marked 

 continental alignement from north to south during the secondary 

 periods. 



There remain to be noticed the great systems of the southern 

 hemisphere, and first that of Australia. Considerable progress 

 has been made by the surveyor of one of the eastern colonies of 



* See Marcou, 'Geology of North America' (Zurich, 1858); his views 

 are, however, repudiated by the American geologists. See Dana, in Silli- 

 man's Journal, vol. xxvi. p. 323. Heyden and Meek in same, vol. xxvii. 

 pp. 35, 219. This overlay of the cretaceous deposits in many parts of the 

 northern hemisphere, together with their great extent there, appears to in- 

 dicate that extensive subsidences in this hemisphere preceded that general 

 change in the geographical alignement which in the third section I propose 

 considering. 



t See Note || , ante, p. 165. 



