460 CALAMITES. 
Torrid Zone, its species are most abundant in 
the temperate zone, decrease in size and num- 
ber as we approach the regions of cold, and 
arrive at their greatest magnitude in the warm 
and humid regions of the Tropics, where their 
numbers are few. 
M. Ad. Brongniart* has divided fossil Equise- 
tacese into two Genera ; the one exhibits the cha- 
racters of living JEquiseta, and is of rare occur- 
rence in a fossil state ; the other is very abun- 
dant, and presents forms that differ materially 
from them, and often attain a size unknown 
among living Equisetacese ; these have been 
arranged under the distinct genus Calamites, | 
they abound universally in the most ancient Coal 
formation, occur but sparingly in the lower strata 
of the Secondary series, and are entirely wanting 
in the Tertiary formations, and also on the actual 
surface of the earth. 
The same increased development of size, which 
in recent Equisetacese accompanies their geogra- 
* Histoire des Vegetaux Fossiles, 2nd Livraison. 
f Calamites are characterized by large and simple cylin- 
drical stems, articulated at intervals, but either without sheaths, 
or presenting them under forms unknown among existing Equi- 
seta ; they have sometimes marks of verticillated Branches around 
their articulations, the leaves also are v^^ithout joints. But the 
most obvious feature wherein they differ from Equiseta, is their 
bulk and height, sometimes exceeding six or seven inches in dia- 
meter, whilst the diameter of a living Equisetum rarely exceeds 
half an inch. A Calamite fourteen inches in diameter has lately 
been placed in the Museum at Leeds. 
