HE AGE OF SOME EXISTING SPECIES OF PLANTS. 817 
has supplied the remains of Salix polaris Wahl., S. cinerea L., and 
Hypnum turgescens Schimp. This small group of plants is of great 
interest in connection with the history of existing species ; their 
remains are preserved in such a manner as to permit the closest 
comparison with living plants. Such an examination shows 
that they differ from each other in no particular. In the post- 
glacial deposits 2 Sk fcc Salia herbacea L. is associated with 
polaris Wahl., as I have already stated. These two willows are 
very closely ed ees indeed been treated as the same — 
unti ahlenberg Sele out. e characters mes separated 
disti : 
1812. One of the m a obvious of the specific distinotions is the 
present all the peculiarities which they possess at the present me 
and the venation and form of the leaves of S. polaris Wah 
io. but is aff foun ae arctic an ciuiae species in oan 
and the pre-glacial ‘speci ns of this cellular plant differ in no 
older a containing the remains of existing species, 
which are found also at Cromer, have recently been readily with 
ened diligence and great success by . Clem ob he 
his determinations, and to accept all of them. His collections contain 
sixty-one species of plants belonging Z forty-six different genera, 
ies identified. bs 0 
and of these forty-seven species have been 1 ed. Slabs of 
clay-ironstone from the beach at Happisburgh contain leaves of 
beech, ot. oak ow materials, however, which h 
existing flor 
Only oo species (Trapa_natans ie) has eS from our 
islands ; alls fruits, which Mr. Reid found abundantly in one 
eenale Gmel., “and Pinus file i are aka at present only 
n Europe, ; two species (Peucedanwn palustre Meench. and Pinus 
Ts aay L.) are found also in $1 beria, whilst five more aia 
