INTRODUCTION, 
3 
and the eastern parts of Kentucky and Ohio. Another great coal formation covers this system 
over most parts of the Green River valley in Kentucky, and the Wabash valley in Illinois, 
and is perhaps connected with the coal formations of the Kaskaskia, Illinois, Rock river, and 
Mississippi about St. Louis. Another coal formation covers these rocks in Michigan, extend¬ 
ing from Saginaw bay south-southwest, as we learn from Dr. Houghton, the Geologist of 
Michigan. This coal formation was not known until the researches of the Geological Survey 
of Michigan were in progress. Another coal formation covers the New-York system of rocks 
in the southwest part of Missouri, and in the Choctaw, Cherokee, and Creek country west of 
Arkansas; on the Arkansas and some of its tributaries, and on that spur of the Rocky 
mountains between the Red river and the Arkansas. This formation does not extend within 
the limits of Arkansas, so far as I know, unless at its northwest corner. 
The Cretaceous formation also covers extensive areas of the New-York system of rocks on 
the Red river, the Arkansas and Missouri, and their tributaries, where they have been 
examined by Dr. Pitcher, Mr. Nicollai, Mr. Featherstonhaugh, myself and others. 
The New-York system of rocks includes the Cambrian and Silurian systems of Murchi¬ 
son ; and as these rocks in North America are so much more extensively developed than in 
Europe, and are so situated that their order of superposition can be easily determined, and 
contain many more genera and species of fossils than the equivalent European rocks ; and as 
we have here many strata that are absent in the Cambrian and Silurian systems, the geogra¬ 
phical name of New-York System has been adopted as appropriate, and as one that will make 
no difficulty in determining geological equivalents. 
The Taconic System. This includes rocks between the Primary and Potsdam sandstone, 
and metamorphic rocks, and occurs more or less extensively developed along the western 
boundary of the Highland primary range. 
The Primary system occupies a small portion of Long and Staten Islands ; forms most of 
the small islands belonging to New-York, in the west part of Long Island Sound, all of New- 
York island, Westchester county, the Highlands, their continuation along the east line of the 
State to Massachusetts, and the mountainous parts of Saratoga and Washington counties. 
There are also some isolated masses of primary rocks, like islands, surrounded by other 
rocks. 
