OP PETRIFACTIONS. 221 



dinate to the greywacke slate, abound more in petrifac- 

 tions. They contain principally some species of madre- 

 porites; also screw-stones, (schraubensteine), which ap- 

 pear to be derived from the coralliolites epithonius, and 

 whole families of terrebratulites, with a few species of 

 turbinites, and striped chamites. 



It appears from the preceding statement, that in ge- 

 neral the different species of transition rocks contain 

 similar petrifactions, and that they are principally dis- 

 tinguished by the number of corals and orthoceratites 

 imbedded in them. 



TLffiTZ ROCKS. 



Fossil organic remains are much more abundant, and 

 more varied in the rocks of this than of the preceding 

 class. We shall enumerate the rocks of this class ac- 

 cording to their relative antiquity, and begin with the 

 lowest or first formed number of the series, which is 

 named. 



I. First Sandstone, or Old Red Sandstone. 

 This rock is characterized by its colour, composition, 

 imbedded minerals, strata with which it is associated, the 

 veins that traverse it, and its position in regard to the 

 other rocks of which the crust of the earth is composed. 

 It rests upon the transition rocks, and is very intimately 

 connected with them, as transitions are to be observed 

 from the one into the other. On a general view, it might 

 be viewed as the newest member of the transition class, 

 rather than the oldest of the flcetz rocks. The red sand- 

 stone contains but few petrifactions, and the&e are princi- 

 pally of trunks or branches of trees, some of which appear 

 to resemble those of the tropical regions. The great coal 

 formation sometimes rests upon this sandstone. In the 



