PETEOGEAPHIOAL CHARACTERS OP MANSFIELD SLATE. 



61 



higher percentage of water contained in the clays. This difference is 

 natural, clays usually containing about twice as much water as do the 

 slates. 



COMPARISON OF ANALYSIS OP MANSFIELD CLAY SLATE "WITH ANALYSES OF OTHER 



CLAY SLATES. 



In the following table there are given, for purposes of comparison with 

 the Mansfield clay slate, analyses of typical clay slates, roofing slates from 

 the Cambrian of Vermont and New York. 



Analyses of typical clay slates. 



Constitnent. 



SiOs 



Ti02 



AI.2O., 



FeiO, 



FeO 



MnO 



CaO 



BaO 



MgO :... 



KjO 



NajO 



H2O at 100° .... 

 H2O above 100°. 



PjOs 



CO: 



reS.> 



c 



60.28 



.69 



22.61 



2.53 



.45 



Trace. 



.13 



.04 



1.35 



5.73 



.54 



.60 



3.62 



.03 



None. 



62.37 



.74 



15.43 



1.84 



5.34 



. 22 



.77 



.07 



3.14 



4.20 



1.14 



.34 



3.71 



.06 



.87 



.06 



Trace. 



67.61 



.56 



13.20 



5.36 



1.20 



.10 



.11 



.04 



3.20 



4.45 



.67 



a . 45 



6 2.97 



.05 



None. 



.03 



67.89 



.49 

 1L03 

 1.47 

 8.81 



.16 

 1.43 



.04 

 4.57 

 2.82 



.77 

 a. 36 

 6 3.21 



.10 

 1.89 



.04 



Total 



S9. 80 



a H2O at 110° 



6 H2O above 110° 



No. 1. Black slate, Sp. 32497, N. 450, W. 1620, sec. 17, T. 43 N., E. 31 W., Michigan. Analyzed by 

 George Steiger. 



No. 2. Sea-green slate, GrifBth & Nathaniel Quarry, South Poultney, Vermont. W. F. Hillebrand. 



No. 3. Black slate, American Black Slate Company, Benson, Vermont. W. F. Hillebrand. 



No. 4. Red slate, three-fourths mile south of Hampton Village, New York. W. F. Hillebrand. 



No. 5. Green slate, three-fourths mile northwest of Janesville, Washington County, New York. 

 W. F. Hillebrand. 



Nob. 2, 3, 4, and 5 taken from Analyses of rocks and analytical methods, 1880-1896, Clark and Hille- 

 brand : Bull. U. S. Geol. Survey, No. 148. Nos. 2 and 3 are, respectively, C and F, p. 277, and Nos. 4 and 5 

 are A and 0, p. 280. 



