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The volume which followsis the third and last of those which constitute the purely geolo- 
gical portion of the report required of the Geological Corps by the organic law of the 
Survey. Material sufficient to form a volume equal in size to the two before published 
was prepared, and its publication was authorized more than three years since, but its ap- 
pearance has been delayed by various causes, chief among which was the rapid develop- 
- ment of the coal and iron industries in the southeastern portion of the State, and the 
important discoveries made during the progress of the extensive explorations under- 
taken in this region.. The eredit of the Survey, and the interests of all those who were 
taking part in the development of the resources of this section, seemed to require that a 
new and thorough survey of at least the Hocking Valley Coal Field should be undertaken. 
This has been done with much care, and with very gratifying and satisfactory results, 
and the pages which follow give ample evidence of the importance and even necessity 
of this re-survey. 
Much work has also been done during the interval in other parts of the State, correct- 
ing errors that have been made, or adding to the facts before gathered. In this way 
the dimensions of the volume now published have been considerably augmented, and its 
value greatly enhanced. It should also be said that the new material added to the 
volume has been acquired at very small cost to the State, assince 1874 no regular 
salaries have been paid to the members of the Geological Corps, and the small sum 
appropriated since the above date has been no more than sufficient to pay the actual 
expenses incurred in field and office work.- Hence the delay has been a gain rather 
than a loss to the people of Ohio. 
Part II of this volume, constituting the third and last contribution to the Paleontology 
of the State, is in the course of preparation, and will be ready for presentation to the 
next Legislature. : 
' Vol. IV, Zodlogy and Botany, is now in the printer’s hands. The Geolagical Map of 
the State will be ready for distribution this year. Vol. V, Economic Geology, is more 
than half done, and it is expected that the material necessary to complete it will be 
added during the coming year. It will be impossible for the public to justly estimate 
VA 
