68 
CLASSIFICATION. 
was necessary to comprise those beds which are 
formed of the comminuted fragments of the primi- 
tive rocks, but which contain few vegetable or ani- 
mal relics. Such a class, therefore, was adopted, 
under the name of intermediate or transition class. 
Still later, owing to the progress of the science, a 
third division was added, called the tertiary. So 
that all the different rocks and strata that cover the 
earth's surface are commonly arranged under the 
following classes : 
1. Primary. 
2. Transition. 
3. Secondary. 
4. Tertiary. 
5. Basaltic and Volcanic* 
6. Diluvial and Alluvial. 
As, however, other classifications have been mad« 
which are often referred to by geological writers, 
it will be necessary to become acquainted with 
them to a certain extent. Conybeare and Philips, 
in their geology of England- and Wales, divide the 
cru&t of the earth into five portions, forming the 
following classes : 
1. The superior, containing the tertiary deposites. 
2. The supermedial, containing the chalk, green 
sand, Wealden, oolitic, and red sand formations. 
3. The medial, containing the coal measures, car- 
boniferous limestone^ millstone grit, and old red sand- 
stone formations. 
4. The submedial^ com^rmng the transition rocks. 
5. The inferior^ containing the primitive rocks. 
M. de la Beebe, one of the ablest geologists of 
the present day, has made the following classifica- 
tion of rocks, whieh has been adopted by many ge- 
ologists as supedo*r to any other. 
1. Stratified Roces. 
iGroup 1. Alluvial — Peat bogs, sands, coral islands. 
&c. 
