PALAEONTOLOGY 59 



but leaves and branches and bits of wood brought 

 down by the rivers and drifted out to sea. Often a 

 slight change of current or a higher tide will cover these 

 scraps with sand or silt, and if they are well covered 

 they are perserved from decay between the layers of 

 fine silt or mud. This is one of the ways fossils are 

 formed. There have been seashores with sand and mud 

 washed up by the waves ever since there have been 

 habitable lands, and from all the epochs of early time, 

 with all their different kinds of plants, there have been 

 fragments here and there preserved on the old sea- 

 shores or in the deposits that once formed the bottoms 

 of lakes or broad rivers. Buried with the mud or sand 

 of these shores and lake bottoms, deposited now here 

 and now there as the physical geography changed, are 

 remnants of the vegetation that was living in the various 

 epochs. Sometimes the local currents favoured the de- 

 position of many plants in one place, and at others 

 there are almost no remains of the local vegetation. 

 From the fragments in the rocks palaebotany pieces 

 together the ancient plants, and in some fortunate 

 cases can discover, not only w r hat they looked like 

 externally, but also the very details of their internal 

 anatomy. 



The aim of palseobotany is to restore the whole series 

 of plants that have lived upon the earth. If that were 

 done completely then there would be no need for the 

 further theorising about past evolution ; we should 

 have before us clear evidence of the actual series of 

 forms through which our recent plants have evolved. 

 But this state of affairs is excessively remote, for at 

 present we have only rescued from the preserving 

 strata of the rocks fragments of the extinct genera. 



These fragments, all of which are called fossils, are 



