492 OVERLYING ROCKS. 



formed all that is expected if it shall hereafter 

 facilitate a more perfect arrangement of the sub- 

 stances which it includes. That the attempt is 

 new, and that the most indescribeable confusion 

 has hitherto reigned among these rocks, will 

 form an apology, not only for the imperfections 

 of this arrangement, but for the great length of 

 the following catalogue. The minuteness of 

 detail which it was thought necessary to adopt, 

 may possibly be dispensed with whenever these 

 rocks shall become more generally understood. 



SYNOPSIS OF THE OVERLYING ROCKS. 



FIRST DIVISION. 



Simple : or apparently simple. 



A. Wacke : of the Germans. Resembles indu- 

 rated clay, with an even and smooth earthy, or an un- 

 even somewhat granular fracture, and a shining streak. 



a. Compact. 



b. Cellular : but generally, in that case, 



partly amygdaloidal, and appertain- 

 ing to another division. 



B. Indurated clay : more or less hard : with an 

 earthy and dull fracture. Much more common in 

 Scotland than the preceding. 



a. Compact. 



