478 OVERLYING ROCKS. 



than have yet been required in treating of any of 

 the preceding. These will be found, either in 

 the following remarks or in the Synopsis, as ap- 

 pears most convenient for elucidating the subject. 

 It must here however be observed, that the 

 terms already in use for distinguishing the several 

 species ? (or varieties,) are neither sufficiently 

 numerous, nor very accurately limited. To have 

 changed the application of these, would have 

 been to depart from the general principles already 

 laid down. Two new terms have however been 

 adopted, those of Hypersthene rock, and Augit 

 rock ; these compounds having been hitherto 

 undescribed, and it being absolutely necessary to 

 distinguish them from the greenstones containing 

 hornblende which they so much resemble. The 

 term wacke has also been admitted ; but with 

 some hesitation ; partly because it did not appear 

 very necessary, and partly because it has been so 

 often misapplied as to be nearly unintelligible. 

 The names adopted therefore, in addition to 

 these three, are claystone, indurated claystone, 

 clinkstone, compact felspar, basalt, greenstone, 

 syenite, porphyry, amygdaloid, and tuff. Trap 



