112 



strata : the appearances which might be mistaken 

 for these, are noticed under the head of veins. 



Pseudo-strata are limited to the rocks of the 

 overlying 1 division, or to the traps, syenites, and 

 porphyries, and to granite. This distinction is 

 practically the most easy ; and it is the only one 

 necessary for the student, if, as is presumed, the 

 observations on which it is founded are correct. 

 If otherwise, it may still remain a rule, until it is 

 proved to be unfounded by a more extensive know- 

 ledge of this subject. 



NODULES. Or imbedded irregular masses. 



This term is adopted, for want of one more 

 appropriate, to include rocks which are not stra- 

 tified, nor disposed in pseudo-strata, and which 

 do not resemble in their connections the large ir- 

 regular masses. 



The form of nodules is very various. They 

 are sometimes extremely irregular, at others 1 , 



i 



bounded by smooth or even surfaces, and possess- 

 ing an average general dimension alike in every 

 part. Not unfrequently , they have a much greater 

 dimension in two directions than a third ; and, in 



