14 
INTERPRETATION OF FOSSIL PLANTS 
deposits usually present obvious characters, both physical and 
botanical. Generally roots are present in the underclays beneath 
coal or lignite beds, so-called mother of coal is present in the 
lignites, and the botanical facies of the preserved species is char¬ 
acteristic. 
Epirotic, or continental, deposits, especially those of eolian 
origin, usually contain few recognizable plant fossils, since wind- 
action is usually at its maximum efficiency in arid regions with a 
seasonal or scant rainfall. A partial exception is afforded by 
the transport of volcanic ashes in quantity which may settle in any 
environment, as for example in the humid, subtropical forests of 
Pliocene age, in Bolivia. Plants of arid regions will be largely 
of a type denominated xerophytic by ecologists. Evaporation is 
checked by reducing the size of leaves, by curling their margins, by 
tomentose, or waxy, surfaces, by thick palisade tissue and re¬ 
duced stomata. Branches may be reduced to thorns and leaves 
to phyllodes or phylloclads. For the detailed physiological re¬ 
sponse of plants to mesophytic, halophytic or xerophytic envi¬ 
ronments the reader is referred to the various texts on ecology and 
plant geography. 
It will be sufficient to mention here some of the features shown 
by the condition of preservation of plant remains in continental 
sediments. Of the various types of sediments, such as lacustrine, 
flood-plain, fluviatile and eolian that go to make up continental 
deposits, the condition of preservation of the contained plants 
furnishes absolute criteria for differentiating between wind- and 
water-laid material. In eolian deposits leaves will be covered in 
a rolled and crumbled or curved condition as they dried. They 
will scarcely ever conform to the bedding of the material and may 
be at right angles to it. Fruits will have lost their outer coats or 
arils, and will be jumbled together at all angles. Cones will have 
their scales separated and distended as in the familiar dried cones 
of our modern conifers. If the deposits be water-laid leaves will 
conform to the bedding because of their water-soaked and limp 
condition, and this limpness may result in minor irregularities of 
surface, but nothing corresponding to that which obtains under 
eolian conditions. Fruits will also conform to the bedding, and 
cones will not be shrivelled with their scales distended. A striking 
instance of position is furnished by the large stones of a species 
