1856.] Physical Geography of North America, 181 



plain on the east ; on the south it was the'southern termination of the 

 Appalachian chain and the other great north-east and south-west 

 palaeozoic tract, west of the present Mississippi ; and on the west, for 

 along distance northward, it coincided generally with the present 

 valley of the Upper Missouri. This cretaceous sea lapped round 

 the southern end of the Rocky Mountains, and spread as far to the 

 west as the Cordilleras of New Mexico and the Wahsatch chain of 

 Utah. We do not at present know that it extended any further. 



The close of the cretaceous or chalk period was marked by the 

 rise and desiccation of nearly the whole now continental area of 

 this great northern Mediterranean. The movement along the 

 Atlantic border of the continent was comparatively slight, for it 

 brought above the sea level only very limited and narrow tracts of 

 the shoal water cretaceous sediments. South of the Appalachian 

 region it was somewhat more extensive, elevating a wider zone 

 between the previous dry land and the newly formed tertiary shore ; 

 but to the west of the region of older rocks it was a broad conti- 

 nental rising, draining dry nearly the whole bed of the then existing 

 ocean to the limit indicated beyond the Rocky Mountains. The 

 coast line established by this lift of the crust, set new and much 

 more restricted bounds westward and northward to the Atlantic 

 ocean, and established the outlines of the present Gulf of Mexico, 

 which thus dates back as far as the commencement of the eocene 

 tertiary age. It does not seem probable that Florida was then any 

 part of the dry land, the true southern peninsula of the continent 

 being rather the newly formed cretaceous plain at the end of the 

 Appalachians. 



From that date, the movements in the level of the continent 

 have been manifestly less and less. Its great outlines, established at 

 the close of the chalk period, have remained as its contour to the 

 present day ; and each successive gain of territory, during the 

 several tertiary revolutions — that which ended the eocene, that 

 which closed the miocene, and that which cut off the pliocene, and 

 even the pleistocene deposits, was but an enlargement of the primi- 

 tive mesozoic pattern, a mere addition of a lighter and lighter fringe 

 to the broad mantle of land, which earlier convulsions had con- 

 structed. 



American Coal Fields. 

 The speaker selected from the many topics presented by this 

 sketch of the geology of North America, that of the coal-fields of 

 the United States and British Provinces, as presenting a theme of 

 general interest, describing first briefly the carboniferous formations, 

 especially their coal measures. 



This formation consists, in the United States and North-eastern 

 British provinces, of argillaceous and siliceous sandstones, conglome- 

 rates, clay shales, fire clays, and coal slates ; argillaceous limestones, 

 chiefly of marine origin, and seams of coal. A coarse siliceous con- 

 glomerate or millstone grit, generally destitute of coal, underlies the 



