88 Seward: The Jurassic Flora of Yorkshire. 
family of conifers which now plays so prominent a part in the 
floras of northern latitudes. Several species of Conifers are 
recorded from British Jurassic beds, but in most cases they are 
represented only by vegetative twigs, and their systematic 
position cannot be determined with any degree of confidence. 
In the foregoing account I have referred only to a selected 
number of types, my object being to emphasise the need for 
more thorough investigation of the rich and important York- 
shire flora, and to give prominence to the fact that the fossil 
plants already obtained from the English strata have afforded 
uncontrovertible evidence as to the remarkable changes in 
the distribution of groups and genera of plants which have 
taken place since the days of the Jurassic period. 
There remains a word to be said on the flora as a whole, 
both as regards the classes which seem to have been most 
abundantly represented as also in regard to conclusions 
deduced from negative evidence. In dealing with an assem- 
blage of plants collected from diflerent strata in a geological 
series, we are usually hampered by insufficient information 
as to the nature of the sediments from which the individual 
specimens were obtained. Our material consists for the most 
part of waifs and strays of a vegetation which happen to have 
been buried in sand or mud, and to have successfully withstood 
the destructive agencies inseparable from geological change. 
We are able to identify with reasonable precision a proportion 
of the specimens, and to form some idea of the relative abun- 
dance of different genera, but we are not, as a rule, in a position 
to say whether all the plants grew together in a similar situation, 
or whether certain specimens had travelled further than others 
before they came to rest on the floor of the estuary or sea. 
Evidence is seldom available which helps us to distinguish 
between the plants of a vegetation which clothed the higher 
ground, and those which lived at a lower level. The point is, 
that we are not justified in assuming an identical habitat for 
all the plants represented in the sedimentary strata exposed 
in the Yorkshire cliffs. It might be possible, by more intensive 
study of the beds in which the specimens occur, to gain some 
knowledge of the grouping of the plant-associations in the 
ancient flora. 
In a region consisting of high ground abutting on a low- 
lying swampy area, we find associations of plants differing from 
one another both in the species characteristic of each, and, it 
may be, also in the structural features which reflect the strongly 
contrasted conditions in the two environments. So in the 
case of fossil plants, we should like to know whether some forms 
may have journeyed far in hill-fed streams, while others may 
have drifted but a short distance from some lower habitat. 
Naturalist 
