Anonymous • The Study of Fossil Plants 



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parts of the world. Sandstone, shale 

 and slate yield an abundant supply of 

 fossilized plants. These, being sedimen- 

 tar}' rocks, are formed from materials 

 that have been washed down from high 

 elevations and deposited in either fresh 

 or salt water during a great "flood." 

 Just how these "floods" (in some in- 

 stances they covered relatively small 

 areas) were caused is an interesting 

 speculation. It is thought that due to 

 movement of the earth's crust, the land 

 subsided and allowed the sea to rush 

 in and cover it. The ordinary process 

 of erosion by the rains, winds, etc., also 

 accounts for some inundations that 

 were destined to preserve plant struc- 

 ture for study during later ages. 



Fossils are also found in volcanic 

 tuff, which is the rock formed from 

 volcanic ashes. Plants falling into min- 

 eral springs were quickly infiltrated 

 with a special kind of limestone and 

 thus were preserved entire. Amber has 

 also been a medium for preserving 

 plants from the far distant prehistoric 

 times. It was formed from the resin of 

 coniferous trees. Parts of plants, and 

 also insects, have been imbedded in the 

 resin which later solidified, thus pre- 

 serving them intact and in their orig- 

 inal state. The color of structures 

 preserved in amber, which is lost 

 through the other types of fossilization, 

 remains unaltered through the ages and 

 gives us our only impressions of the 

 colors in the prehistoric forests. 



Many fossil plants are found in the 

 so-called coal balls. These are hard 

 dark lumps which are found in coal 

 seams. They vary in size from small 

 masses approximately one or two 

 inches in diameter to those a foot or 

 more in diameter. On examination 

 these coal balls prove to be masses of 

 plant material saturated with crystal- 

 linic lime. The deduction is that at the 

 time the coal seam was formed, some 

 mineral water in the coal swamp pre- 



cipitated lime cr\stals or silica about 

 the nucleus of plant matter, which 

 through this process has been preserved 

 almost in its original form. 



We cannot, within the limitations 

 imposed by a short article, enter into a 

 detailed account of all of the plants 

 that flourished during the Coal Age. 

 However, we will give below a brief 

 description of some of the major forms. 



SPHENOPSIDA 



This group includes among others, 

 the Paleozoic Calamites, the remote 

 ancestors of our present day horsetails 

 or scouring rushes. Quite in contrast 

 with the small American scouring 

 rushes, which are to be found earlv in 

 the year along the banks of brooklets 

 and other moist places, were the giant 

 Calamites, which in general appear- 

 ance resemble extant horsetails but 

 which attained heights of a hundred 

 feet. They bore narrow lance-shaped 

 leaves arranged in whorls at the nodes, 

 just as the present forms possess scale- 

 like leaves in a circular arrangement 

 about the nodes. The stems of these 

 giant horsetails were hollow. Most of 

 the plants of this group must have been 

 arborescent although there must have 

 been herbaceous species as well. 



Calamites are found in the Penn- 

 sylvania deposits and are very abun- 

 dant in the coal deposits in the east- 

 ern United States. They disappeared in 

 the Permian. 



LYCOPSIDA 



The surviving genera of this order 

 are our present day club mosses 

 Lycopodium (commonly called ground 

 pine), Selaginella, Isoetes and others. 

 Lepidodendron and Sigillaria are the 

 principal genera of Paleozoic Lycop- 

 sida, about 100 species of each having 

 been described. Both of them attained 



