622 GEOLOGY OF OHIO. 



abruptly into a very rough and ungainly stone, called "Turtle-back," or 

 "Nigger-head," by the quarrymen. Their surfaces in such instances are 

 generally covered with marks, indicating origin in shallow water. They 

 are destitute of lines of bedding, and present rather the appearance of 

 concretionary structure than of deposited layers. Such courses are al- 

 together valueless as building stone, and are used only for the protection 

 of river banks and for other similar purposes. The large amount of waste 

 material to be moved in reaching the most reliable and desirable courses 

 constitutes the main element in the expense of quarrying. In the Jas- 

 per quarries, for example, not more than ten feet of the thirty feet that 

 belong,' to the system can be put into the market as first-class building 

 stone. 



Of the many shades of color displayed by the Waverly quarry courses, 

 perhaps a light drab can be taken as the standard ; at least it is the 

 color which is most highly esteemed for architectural purposes. It is 

 not, however, an original color of the stone, but has been formed by the 

 action of the atmosphere on the external portion of the'exposed layers. 

 The native color of the beds from which this most approved variety is 

 derived is a delicate blue — a little deeper than the shade known among 

 painters as French gray. By the oxidation of some of its materials, or, 

 possibly, by the removal in solution of a small portion of oxide of iron, 

 the change is effected. The very slight difference in composition be- 

 - tween the weathered, or bleached portion, and the blue stone, is shown 

 in the following analysis made by Prof. Wormley. The samples taken 

 for analysis were from the quarries of Maurice Reiche, Esq , of Waverly, 

 who has made a very careful study of the building stones of the Scioto 

 valley, and to whom the Survey is indebted for much valuable informa- 

 tion: 



No. 1. So. 2. 



(White stone.) (Blue stone.) 



Silicic acid 91.30 91.00 



Protoxide of iron 0.86 1.17 



Sesquioxide of iron 0.06 0.30 



Alumina 5.79 5.20 



Lime trace trace 



Magnesia '. 0.32 0.28 



Water, combined 1.30 1.80 



99.63 99.75 



The change from the blue color to the lighter tint has taken place in 

 all exposed portions of the rock, but seldom extends inward more than ten 

 or twelve feet. As these weathered portions have been first removed, 

 not only on account of the desirability in color, but also by reason of 



