172 



GEOLOGY. 



few of either class are found among the fossils of the far 

 past, but the record of life in the rocks shows that they 

 were more and more introduced the nearer we come 

 down to the age of man in tracing the successive ages. 



254. Investigation of Vegetable Fossils. We can not 

 study fossil botany in the same manner that we do the 

 botany of the present. In the latter case we have all the 

 parts of plants in full, but in the former merely remains, 

 and sometimes only scanty ones. In many cases, there- 

 fore, in fossil botany we can only approximate to a true 

 classification. With the scanty evidence often present- 

 ed, it is not surprising that some mistakes should have 

 been made. One of these I will mention. For a long 

 time certain trunks of trees found in the coal measures 

 were put in a different family from certain roots found 

 also in these measures; but at length it was discovered 

 that the roots and the trunks belonged to the same tree, 



though in the stra- 

 ta they were found 

 separated from each 

 other. Of the many 

 points of distinction 

 in regard to vegeta- 

 ble fossils I will no- 

 tice but one, the ve- 

 nation of leaves, 

 or the mode of dis- 

 tribution of their 

 veins. The veins 

 in the leaves of en- 

 dogenous plants 

 run parallel with 

 each other, as seen 

 in Fig. 92, while in 

 the exogenous the 

 veins interlace, as seen in Fig. 93, which represents the 

 leaf of the apple. 



