54 
EQUISETACE^. 
dence to shew the presence of a hotter cli¬ 
mate during the formation of earlier de¬ 
posits. These fibrous coverings^ so bene- 
hcal to the earth under a low temperature, 
are neither found nor required in tropical 
regions. 
III. The third class is of great geological 
interest, the Equisetacecc. One of its families 
is known to us in this country by its re¬ 
presentative growing in our meadows, the 
Horse-tail, a little cane-like plant rising 
amidst the grass in the ditches, and attaining 
a few feet in heighth, which is increased to 
a maximum of twelve feet in equinoctial 
marshes. In the Lias, the blue building 
stone of north-east Yorkshire, are vertical 
stems of a similar kind, and they are also 
sparingly found in the coal measures. But 
our little marsh plant is more abundantly 
represented by the numerous calamites of 
the coal. Jointed cylinders with frequent 
divisions, and corduroy-like stripes, once 
hollow and succulent, but now flattened and 
filled wdth sandstone, are common at nearly 
every pit’s mouth in the carboniferous dis¬ 
trict, and are even distinguishable amidst 
