PORTAGE COUNTY. 137 



GEOLOGICAL STRUCTURE. 



The number and relative positions of the strata which come to the 

 surface within the limits of Portage county will be seen at a glance by 

 reference to the section given below : 



FT. 



1. Superficial clay and gravel 10 to 100 



2. Shale and sandstone 50 



3. Limestone to 4 



4. CoalNo.4 1 to 5 



5. Fire-clay 3 to 4 



6. Shale and sandstone 25 to 30 



7. Limestone Oto 4 



8. CoalNo.3 1 to 3 



9. Fire-clay ; 3 to 12 



10. Shale 20 to 50 



11. CoalNo.2 Oto 1 



12. Sandstone 50 to 100 



13. Shale Oto 50 



14. CoalNo.l Oto 5 



15. Fire-clay 3 to 5 



16. Shale and sandstone 25 to *50 



17. Conglomerate 100 



All the rocks enumerated in the preceding section belong to the Car- 

 boniferous system, of which they lepresent two members, viz., the Con- 

 glomerate and the Coal Measures. The area of the county is about 

 equally divided between the two formations. All the northern half has 

 the Conglomerate for its surface rock, though it is generally deeply 

 buried by Drift clays. It is fally exposed in the valleys of the Mahoning 

 and Cuyahoga. The trough of the latter stream is cut in the Conglom- 

 erate all the way from the point where it enters the county, in Hiram, 

 to its place of exit, on the west side of Franklin. The Conglomerate is 

 well seen in Mantua and Garrettsville, and still better in Franklin and 

 Nelson. In all these localities it exhibits essentially the same charac- 

 ters, viz., a coarse, drab-colored sandstone, in places thickly set with 

 quartz pebbles from the size of a pea to that of an egg. In some places, 

 as in Windham, the stone it furnishes is finer, whiter, and more homo- 

 geneous, and would answer admirably for architectural purposes. As a 

 general rule, however, it is rather coarse for all fine work, but furnishes 

 a strong and durable stone, well adapted to bridge-building, cellar walls, 

 and, indeed, to all plain and massive masonry. 



Near Kent certain layers of the Conglomerate have been found, which 

 are white enough to serve for the manufacture of glass. The coloring 

 matter of the rock is usua,lly iron, and it here contains much less than 

 usual. 



