460 SHALE. 



SYNOPSIS OF SHALE. 



FIRST DIVISION. 



Simple. 



A. Common shale. 



a. Hard, and often not distinguishable 



from the fine and the coarse and 

 argillaceous schists of the primary 

 class: namely, clay slate, and ordi- 

 nary graywacke. 



This variety occurs chiefly with the lowest or 

 red sandstone 



b. Somewhat fragile, and less continu- 



ously laminar. 



Occurs in alternation with the superior sand- 

 stones, or with the secondary limestones, or with 

 common clay. 



c. Tender, often scaly rather than laminar. 

 Occurs in similar situations, where it is fre- 

 quently the repository of organic remains. 



d. -Passing into clay. 



e. Granular concretionary : occurs, hi- 



therto, only in the Shiant Isles. 



f. Spheroidal concretionary : in the same 



situation : in the vicinity of trap. 



The prevailing colours of these shales are 

 various shades of grey, commencing from black 



