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there occurs a remarkable succession of Loess hills. The country 

 rock of central and southern Iowa is Carboniferous. The north- 

 ern portion is covered so deeply by the drift mantle that the 

 country rock does not or rarely comes to the surface. The to- 

 pography of the State is prevailingly that of the drift period with 

 the changes effected by subsequent erosion. 



The fern flora of Iowa is not extensive. Yet, when the great 

 uniformity of the surface features of the State are considered, 

 the flora is all that could be reasonably expected, and probably 

 more. The forty-seven species — thirty-one ferns and sixteen 

 allies — enumerated below are but a mere remnant, the last suc- 

 cessors, of a magnificent fern forest which culminated and 

 reigned supreme in Iowa during the Carboniferous era or of the 

 profusion of ferns to be expected during the Eocene when forests 

 were abundant and a tropical climate prevailed, or during the Af- 

 tonian, an interlude between two great ice invasions, when conif- 

 erous forests grew in plenty. Our fern flora has been destroyed 

 and rebuilt many times ere we reach the present epoch. Each 

 succeeding flora was made up of different species of less magnifi- 

 cence and in diminished numbers. At the close of the Pleistocene 

 the fern's position in the biologic world was lowly, being few 

 in number and small in stature. During this time the mastodon 

 and the elephant roamed at will over our prairies and by our 

 rivers and gathered their sustenance from our grassy savannas. 



Geologic history now closes and modern Iowa comes forth 

 with our present fauna and flora. Deciduous forests appear along 

 our border rivers and their tributaries. The extent of the forests 

 is moderate, the greater portion of the State being prairie. The 

 ferns are found as mesophytic species only in the woodlands or 

 as xerophytes in the crevices of rocky cliffs. The woodland 

 species are diminishing in number of individuals as the forests 

 are being displaced as a result of agricultural pursuits. The cliff 

 species are holding their own. 



Within our borders the bulk of the species is limited to the 

 eastern half of the State ; the western portion having few ferns, 

 there being few rock exposures and only a scanty tree growth. 



A study of the Iowa fern flora reveals the fact that there 

 must have been a more extensive one in recent times. The iso- 



