292 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



There are many horizons of limestone in these two divisions of the 

 Coal Measures. The Limestones are of fresh water origin in the main, 

 are readily soluble in atmospheric waters, and give rise by their decay 



to soils of unusual fertility. It: thus happens that the hills of this por- 

 tion of the State rank as high in agricultural wealth as the plains and 

 valleys of the west rrn half of the State. Soineof the limestones of this 

 series yield natural hydraulic cements of fair quality. 



In the vicinity of Barnesville ?i ■'-'- the highest rocks of the Ohio scale 

 are found. They have been proved by Fontaine and White, by means 

 of their flora, 84 to have a Permian aspect, but having much in common 

 with the underlying division they arc generally recognized as a transi- 

 tion series under the name Pormo-Oarboniferons. 



At Cambridge the railroad reaches the uppermost seam of the Lower 

 Coal Measures of the State, the Upper Freeport Seam. A coal field 

 of great importance begins at this point and extends for many miles to 

 the southward and southeastward. Within the limits of this field the 

 deepest-lying coal of the State is likely to be found. The seam has 

 been followed by the drill to a depth of at least 500 feet (152 m.) below 

 the valley levels to the southeastward. This coal has an excellent 

 reputation as a steam coal. It has a maximum thickness of 7 feet, but, 

 more than any other Ohio coal, it is liable to disastrous u wants" or 

 u cutouts," due to its invasion by the great Mahoning sandstone, which 

 is the next higher element in the normal section. A low anticline 

 traverses the series near Cambridge which has proved effective in the 

 accumulation of gas and oil to a small extent. The reservoir rock is 

 the Berea grit, which here lies about 1,000 feet (.504 m.) below the sur- 

 face. A very important oil field is found at Maeksburg, .'JO miles (48 

 km.) south of Cambridge. 



At Zanesville l: -'"- M two of the most important coal seams of the lower 

 measures, the Lower and Middle Kittanning seams, are extensively 

 mined. They underlie much of the town and are well developed in the 

 surrounding country. A score of miles to the southwest ward they con- 

 stitute the Hocking Valley coal held which is now producing 5,000,000 

 tons annually and which is decdedly the most important coal held of 

 the State. 



Fire clays and shales are found associated with the coal seams in 

 large amounts. They are proving far more valuable than the coals 

 themselves, constituting as they do an excellent basis for the mann 

 facture of building brick of all qualities, of paving brick (vitrified), of 

 earthenware, and finally of encaustic tiles of the finest quality, The 

 American Tile Works established here are the largest of their kind in 

 the world, employing a thousand men and furnishing a product that 

 competes successfully in the New York markets with the best grades of 

 imported floor and ornamental tiles. Zanesville is the most important 



