8 KEMP'S ORE DEPOSITS. 



land and northern New York the Archaean is especially devel- 

 oped, forming the White Mountains, the Adirondacks, and the 

 Highlands of New York and New Jersey. These all consist of 

 granite and other igneous rock, of gneiss, and of crystalline schists. 

 There are also great areas of metamorphic rocks whose true age 

 may be later. The Green Mountains are formed of such, and were 

 elevated at the close of the Lower Silurian. In New England there 

 are small, scattered exposures of the undoubted Paleozoic (Devo- 

 nian, Carboniferous). In eastern New York, and to some extent in 

 New Jersey and eastern Pennsylvania, the entire Paleozoic, except 

 the Carboniferous, is strongly developed. Up and down the coast 

 there are narrow north and south estuary deposits of red Jura-Tri- 

 as sandstone, which are pierced by diabase eruptions. The Creta- 

 ceous clays are strong, and Tertiary strata occur at Martha's Vine- 

 yard, in Massachusetts, while over all as far south as Trenton is 

 found the glacial drift. Between the Archaean ridges of the High- 

 lands and the first foldings of the Paleozoic on the west is found 

 the so-called Great Valley, which also runs to the south and is a 

 very important topographic and geologic feature. It follows the 

 outcrop of the Siluro-Cambrian limestones, to whose erosion it is due. 



II. Eastern- Middle and Southeastern Coast District. The 

 low plains of the coast are formed by Quaternary, Tertiary, and 

 Cretaceous, consisting of gravel, sand, shell beds, and clay. In- 

 land there are exposures of Jura-Trias, as in the north. The Ar- 

 chaean crystalline rocks are also seen at numerous points not far 

 from the ocean. Florida is largely made up of limestones, with a 

 mantle of calcareous sand. 



III. Alleghany Region and the Central Plateau. The Ap- 

 palachian mountain system, from New York to Alabama, con- 

 sists principally of folded Paleozoic (largely Carboniferous), with 

 Archaean ridges on its eastern flank. There is an enormous devel- 

 opment of folds, with northeast and southwest axes. On the west 

 they are succeeded by the plateau region of Kentucky and Tennes- 

 see, chiefly Paleozoic. Along central latitudes the Archaean does 

 not again appear east of the Mississippi. 



IV. Region of the Great Lakes. In Michigan, Wisconsin, and 

 Minnesota the Archaean rocks are extensively developed, both 

 Laurentian and Huronian. Around Lake Superior are found the 

 igneous and sedimentary rocks of the Keweenawan, followed by 

 the lower Paleozoic. Lake Michigan and Lake Huron are sur- 

 rounded by Silurian, Devonian, and Carboniferous; Lake Erie, by 



