CHAP. VI.] 



FOSSIL PLANTS. 



189 



feeble attempt at extension about the commencement of 

 the Tertiary period, gradually diminish in importance 

 up to the present time. 



Equisetacece. 

 The horsetails and their allies, amongst the earliest 





Fig. 56. Neuropteris heterophylla, a fossil fern belonging to the 

 Carboniferous period. (Natural size. ) 



of Vascular Cryptogams, appear late in the Silurian, 

 attain their maximum in the Carboniferous, and then 

 gradually decrease, being represented at the present day 

 by only one genus, including about twenty- five species ; 

 these are marsh plants of diminutive size and degraded 

 structure as compared with their forest- forming pro- 

 genitors of the Carboniferous period, such as Calamities*. 



