€84 KEPORT— 1886. 



are represented by the intervening sedimentary deposits. During these alterations 

 of temperature, extensive changes in the configuration of the land vsrere taking 

 place. The first great upheaval occurred in the early glacial period, and was 

 followed by a considerable subsidence. A second upheaval took place late in the 

 glacial epoch. Various estimates have been formed of the time required for this 

 succession of climatic conditions and earth-movements. The moderate computa- 

 tion of Ramsay and Lyell gives to the boulder clay of the first glacial period an 

 age of 250,000 years, estimating the time of the first upheaval as 200,000 years 

 ago, while the subsidence took place 50,000 years later, and the second upheaval 

 92,000 years ago. 



The sedimentai'y deposits later than the Pliocene strata, but older than the 

 glacial drift, indicate an increasing severity in the climate, which reached its 

 height in the first glacial period. 



At Cromer, on the Norfolk coast, the newest of these deposits has supplied the 

 remains of Salix polaris, Wahl., S. cinerea, L., and Hypnuni turf/escens, 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 fi'om each other in no particular. Tn the post-glacial deposits in Sweden, 

 Saliv fierbacea, Ti., is iiSSOcia,ted with S. poltifis, Wa,h.\., na I have already stated. 

 These two willows are very closely related, having indeed been treated as the 

 same species until Wahlenberg pointed out the characters which separated them 

 when he established .SaZi'r joo/arw as a distinct species in 1812. One of the most 

 obvious of the specific distinctions is the form and venation of the leaf, a character 

 which is, however, easily overlooked, but when once detected is found to be so con- 

 stant that it enables one to distinguish without hesitation the one species from the 

 other. The leaves of the two willows in the Swedish bed present all the pecu- 

 liarities which they possess at the present day, and the venation and form of the 

 leaves of S. polaris, Wahl., from the preglacial beds of Cromer present no 

 approach towards the peculiarities of its ally S. herhace.a, L., but exhibit them 

 exactly as they appear in the lining plant. This is the more noteworthy as the 

 vegetative organs supply, as a rule, the least stable of the characters employed in 

 the diagnosis of species. The single moss (Hypnum turgescens, Schimp.) is no 

 longer included in the British flora, but is still found as an arctic and alpine species 

 in Europe, and the pre-glacial specimens of this cellular plant differ in no respect 

 from their living representatives. 



The older beds containing the remains of existing species, which are found also 

 at Cromer, have recently been explored with unwearied diligence and great success 

 by Mr. Clement Reid, F.Gr.S., an officer of the Geological Survey of England. To 

 him 1 am indebted for the opportunity of examining the specimens which he has 

 found, and I have been able to assist him in some of his determinations, and to 

 accept all of them. His collections contain sixty-one species of plants belonging 

 to forty-six different genera, and of these forty-seven species have been identified. 

 Slabs of clay-ironstone from the beach at Happisburgh contain leaves of beech, 

 elm, oak, and willow. The materials, however, which have enabled Mr. Reid to 

 record so large a number of species are the fruits or seeds which occur chiefly in 

 mud or clay, or in the peat of the forest-bed itself. The species consist mainly of 

 water or marsh plants, and represent a somewhat colder temperature than we have 

 in our own day, belonging as they do to the arctic facies of our existing flora. 



Only one species {Trapa nntans, 1j.) has disappeared from our islands; its 

 fruits, which Mr. Reid found abundantly in one locality, agree with those of the 

 plants found until recently in the lakes of Sweden. Four species (Prunics spinosa, 

 L., CEnanthe Lachenulii, Gmel., Fotamogeton heterophyllxis, Schreb., and Finns 

 Abies, L.) are found at present only in Europe, and a fifth {Potamoyeton trichoides, 

 Cham.) extends also to North America ; two species {Peucedanutn palustre, 

 Moench, and Pinus sylvestris, L.) are found also in Siberia, whilst six more 

 {Sangtiisorba officinalis, L., Rubus fruticosus, L., Cornus sanguinea, L., Euphoi-hia 

 mnygdaloides, L., Quercits Robur, L., and Potamogeton crispus, L.) extend into 

 Western Asia, and two (Fagus sylvaticn, L., and Alnus glutinosa, L.) are included 



