334 
EXTENT AND NUMBER OF SPECIES. 
size from a line to more than four feet in di- 
ameter.* 
peculiar to the Lias ; the A. Goodhalli to the Greensand ; and the 
A. Rusticus to the Chalk. There are few, if any, species which 
extend through the whole of the Secondary periods, or which 
have passed into the Secondary, from the Transition period. 
The following Tabular Arrangement of the distribution of 
Ammonites, in different geological formations, is given by Pro- 
fessor Phillips in his Guide to Geology, 1834, p. 77. 
SUB-GENERA OF AMMONITES. 
LIVING SPECIES. 
o 
o 
r'3 
< 
._3 
• 
S 
< 
c 
5- 
a 
O 
"5 
c 
Oh 
a 
o 
Q 
c 
p 
c 
r ^ 
O- 
a 
o 
a 
£ 
a; 
Q 
• 
O 
"7: 
c 
0) 
:jh 
In Tertiary strata .... 
In Cretaceous system. 
2 4 
Q 
14 
13 
9 
3 
In Oolitic system .... 
• • 
• • 
• k 
22 27 
12 
26 
5 
11 
11 
11 
4 
5 
3 
In Saliferous system . 
In Carboniferous sys- 
• • 
3 
i2 
tem 
7 
17 
I In Primary strata. . 
<< 
Total, 223 species. 
It is easy to see how important, in questions concerning the 
relative antiquity of stratified rocks, is a knowledge of Ammo- 
nites, since whole sections of them are characteristic of certain 
systems of rocks." — Phillips's Guide to Geology, 8 vo. 1834, sec. 82. 
X The strata here termed -primary are those which, in the 
Section, (PI. 1), I have included in the lower region of the tran- 
sition series. 
* Mr. Sowerby (Min. Conch, vol. iv. p. 79 and p. 81,) and 
Mr, Mantell speak of Ammonites in Chalk, having a diameter 
of three feet. Sir T. Harvey, and Mr. Keith Milnes, have re- 
cently measured Ammonites in the Chalk near Margate, which 
exceeded four feet in diam.eter; and this m cases where the 
diameter can have been in a very small degree enlarged by 
pressure. 
