CLASSIFICATION OF DEPOSITS. 113 



to be sedimentary deposits, altered by heat ; resembling 

 the plutonic or unstratified rocks in being destitute of 

 fossils, but differing from them in presenting marks of 

 stratification. 



IV. At other points we find, in similar situations, the 

 aqueous or fossiliferous strata, characterised by stratification 

 and the presence of fossils. 



ARRANGEMENT OF DEPOSITS. At an earlier period of the 

 science, the arrangement and nomenclature of the rocks, 

 with reference to their order and succession, were determined 

 as follows : 



The plutonic and metamorphic rocks bore the general 

 name of primitive, it being supposed that they were formed 

 before all others. The deposits lying immediately above 

 them, from resembling the schistose rocks below, in their 

 crystalline texture, while they bore a similarity to the sedi- 

 mentary substances above, in exhibiting proofs of mechanical 

 origin, and containing organic remains, were conceived to 

 form an intermediate class, and the name of transition rocks 

 was accordingly employed to distinguish them. The succeed- 

 ing strata, up to the chalk, were termed secondary, and all 

 above the chalk were named tertiary formations. The 

 progress of geological inquiry, however, soon brought facts 

 to light which produced a considerable change in this nomen- 

 clature. It was found that the so-called primitive rocks 

 were, in fact, of various ages ; that some had been erupted 

 as late as the close of the secondary, and others during the 

 tertiary period, having penetrated and altered, strata of 

 that date. That the so-termed transition strata were, in 

 like manner, of various geological dates and characters, 

 and the result has been the adoption of the arrange- 

 ment now generally received, by which the primitive rocks, 

 as they were previously termed, are distinguished as plu- 

 tonic, or unstratified, and metamorphic, or stratified ; while 

 the term transition is virtually abolished, and the whole 

 series of fossiliferous deposits, from the earliest up to the 

 chalk, are termed secondary ; the inferior beds up to the 

 carboniferous series being sometimes styled the lower ; those 

 from the carboniferous system to the oolite, the middle ; and 

 the wealden and chalk, the upper ; the strata which overlie 

 the chalk being named tertiary ; while the loose and super- 



