18 Geology of the Muskingum Valley. 



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must have been at a period when the whole valley was covered with 

 water^ and before the present hills were formed. The annexed sec- 

 tion will give a better view of its location. 



Fig. 1 



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Explanation.— a, Ohio rivQV.—b, Alluvion or Ohio bottoms,— c. River hill. 

 d, Run and branches.—^, We]].—/, Adjaceqt hills, norlh,—^, Base of the hills 

 on a level with the bed of the river. 



Grotto of Plants. 



At the southern outlet of the Muskingum valley, two miles below 

 the mouth of the river, and forty rods from the bank of the Ohio, 

 an interesting grotto, has been formed in the sandstone from the 

 gradual disintegration of the rock by a chemical process. The 

 rock is rather coarse grained, and is composed of siliceous sand, 

 silver colored mica in minute scales, with lime as a cement, which 

 probably by the aid of the elements of the atmosphere generating 

 nitric acid has formed a nitrate of lime, as the rock itself for a con- 



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siderable depth, as well as the surface is impregnated with these 

 saline particles ; thus it slowly effloresces, and at the same time 

 crumbles away, dislodging and throwing down minute grains of the 

 rock. Irregular veins of argillaceous stone, like hardened clay which 

 are not so readily decomposed, are disseminated through the rock 

 and stand out, In bold relief, from the surface, while °cells of all 

 sizes, from an inch, to six or eight inches in diameter, and as many 

 in depth, are thickly scattered amongst these projecting portions. 

 The roof of the grotto is particularly rich in this natural " fret work," 

 giving it the appearance of an immense honey comb. In the 

 center, the roof Is about twenty feet high, and slopes gradually 

 down to the aoor on the back side, to both extremities ; which are 

 about one hundred feet distant. It is twenty feet in depth. The 

 side next the river, for twenty five or thirty feet, presents a per- 

 pendicular face, on which the decomposing process is now most 

 active. It is free from argillaceous fragments and is of a light ash. 



