SLATES. 313 



was made for me by Mr. Hambly in the laboratory of 

 Dr. Percy at the School of Mines with the following 

 result: 



ANALYSIS OF SLATE. 



Dark SlaJe, two analyses, 



1. Percentage of iron 5.85 



2. " " 6.13 



Mean . . 5.99 



Whitish Green Slate. 



1. Percentage of iron 3.24 



2. " " 3.12 



Mean . . 3.18 



According to these analyses the quantity of iron in the 

 dark slate immediately adjacent to the greenish spot 

 is nearly double the quantity contained in the spot 

 itself. This is about the proportion which the mag- 

 netic experiments suggested. 



Let me now remind you that the facts brought 

 before you are typical each is the representative of 

 a class. We have seen shells crushed; the trilobites 

 squeezed, beds contorted, nodules of greenish marl 

 flattened; and all these sources of independent testi- 

 mony point to one and the same conclusion, namely, 

 that date-rocks have been subjected to enormous pres- 

 sure in a direction at right angles to the planes of 

 cleavage. 



In reference to Mr. Sorby*s contorted bed, I have 

 said that by supposing it to be stretched out and its 

 length measured, it would give us an idea of the 

 amount of yielding of the mass above and below the 

 bed. Such a measurement, however, would not give 

 the exact amount of yielding. I hold in my hand a 

 specimen of slate with its bedding marked upon it; the 

 lower portions of each layer being composed of a com- 



