682 
GEOLOGICAL MAP. 
following gentlemen. Dr. David Dale Owen, the State geologist of Indiana, has permitted me to copy his maps of that 
State and of Illinois, Kentucky and Wiskonsan, including the lead-bearing region of Iowa, into which his researches 
have extended. Dr. Houghton, the State geologist of Michigan, has obligingly furnished me with a geological map of 
that State, where my own observations have not extended far beyond the lake shores. In laying down the formations in 
Ohio, I am indebted both to the reports of Dr. Locke, Mr. Whittlesey, Mr. Briggs and Mr. Foster, and to personal in¬ 
formation from these gentlemen. The valuable paper of Dr. Hildreth, in the 29th vol. of Silliman’s Journal, has also been 
of great service to me. In coloring the map of Virginia, Mr. Slade, a member of the geological corps of that State, has 
pointed out to me the general limits of the formations in the western part. Prof. J. T. Ducatel, the geologist of Maryland, 
has kindly furnished me with the outlines of the formations in that State; and Prof. J. C. Booth, the geologist of Dela¬ 
ware, has afforded me the same facilities. To Richard C. Taylor, of Philadelphia, I am indebted for a colored map of the 
eastern part of that State, recording his own observations previous to the year 1834. This map shows very minutely the 
position and extent of the detached or outlying coal basins on the northeast, and the eastern limits of the great Alleghany 
coal-field. Mr. Taylor has spent many years in investigating this region, and particularly the position and extent of the 
coal-fields, and no one is better able to give the geology of this portion of the country. 
The numerous and frequently alternating strata along the eastern margin of this great coal-field, as well as of the form¬ 
ations farther east, could not be represented on a map of this scale without going into an extent of detail incompatible with 
the present object; in many instances where two rocks are colored alike, they are marked by letters which will indicate 
the formations by referring to the corresponding letters in the index of colors. Bordering the Atlantic south of Dela¬ 
ware, one color only has been used, from the impossibility at present of giving the exact lines of demarkation. The ex¬ 
istence of some minor axes within the limits of the great eastern coal-field, and the appearance of lower formations, have 
not been noticed on the map, as their limits could not be accurately laid down without a more minute survey than I have 
been able to make. * After leaving the western extremity of Lake Erie, the Niagaria limestone, the Onondaga-salt 
group, and the Helderberg limestones are so blended that it has been found impossible to define their limits by the same 
colors as in New-York; the blue, indicating the latter series, is therefore continued as a representative of the whole 
through Ohio, Indiana and Illinois. The area colored of a deeper blue, with a margin of slate color, of which Cincinnati 
is near the centre, represents the Birdseye and Trenton limestones of New-York and also the equivalents of the Utica 
slate and Hudson-river group, the latter having become so calcareous that it is known throughout the west as the Blue 
limestone. + The purple band, indicating all that remains of the formations between the Corniferous limestone and 
the Portage group in Ohio and Indiana (the black bituminous shale) , represents these as terminating before reaching the 
Rock river in Illinois. It is possible, however, that this shale may be traced farther westward, although it was not ob¬ 
served in my examinations along the Mississippi. 
The difficulties encountered in completing this map for publication have not been few, and I cannot flatter myself that it 
is free from error ; I appeal therefore to my friends and a generous scientific public for their forbearance, hoping that some 
future opportunity may enable me to offer it to them much improved and corrected; and in the mean time any information 
or suggestion will be gladly received. A geological map of the remaining portion of the United States is in preparation, 
and will soon be completed. This map will exhibit the limits of the principal formations east of the Mississippi, and be¬ 
tween the Gulf of Mexico and the Great lakes. 
In the present map the wide and almost undisturbed range of some of the lower formations is well illustrated, and the 
immense extent of the two well known American coal-fields seems almost incredible. The great Illinois coal-field occupies 
a space nearly as large as the whole of Great Britian; and the eastern one, occupying a part of Pennsylvania, Maryland, 
Virginia, Ohio, Kentucky, Tennessee and Alabama, is even much larger, occupying an area of sixty thousand square miles. 
These vast formations, with associated iron ores, prove the existence of those sources of wealth, prosperity and civilization, 
which invite to enterprise and reward with plenty. Although not strictly appertaining to asurvey of New-York, sheis still 
not an idle spectator of the vast possessions of the west; she stands upon the vantage ground, and the great mart of the 
Atlantic is only reached through her lakes, her rivers and canals. The immense territory north of the Ohio river, occu- 
* Since this map was engraved, a geological map of the western States has been published by Mr. Byrem Lawrence. The main features of the 
two maps are in accordance, but there are some points in which I have felt authorized to differ from Mr. L. in regard to the limits and extent of 
certain formations. t See Chapter XXII I. 
