ROCKS AND STRATA. yal 
1. The Tertiary ; comprising the deposits between the 
Chalk and the superficial Drift and modern Alluvium. 
2. The Seconpary ; from the Chalk to the Trias or New 
Red, inclusive. 
3. The Patzozoic ; from the Permian to the Silurian; 
including the vast series of unfossiliferous slate rocks termed 
the Cambrian, in which all traces of organic remains are 
lost. 
In the following arrangement the strata are enumerated 
as if lying in regular sequence, one beneath the other ; but 
in nature such an unbroken series has never been observed. 
A few groups only occur in a serial order, and these but 
rarely in their original position. The beds are for the 
most part disrupted, and lie in various angles of incli- 
nation; sometimes they are completely retroverted, the 
newer strata underlying those upon which they were origi- 
nally deposited. The order of succession has been ascertained 
by careful observation of the relative super-position of the 
respective members of the series in different countries ; and 
from an immense number of facts collected by able observers 
in every part of the globe. 
This synopsis presents a chronological arrangement of 
the rocks according to the present state of geological know- 
ledge, but it must not be supposed that these rigid distinc- 
tions, these hard lines, which are necessary to facilitate the 
acquisition of a general idea of the phenomena attempted to 
_be explained, exist in nature. By whatever names we 
designate geological periods, there appear to be no clearly 
defined boundaries between them in reference to the whole 
earth : such well marked lines may be seen in particular 
localities, but daily experience teaches us that there is a 
blending, and a gradual and insensible passage, from the 
lowest to the highest sedimentary strata, particularly in 
respect of fossil remains. The terms employed to desig- 
nate formations can only be considered as expressing the 
