12 MISS M. E. J. CHANDLEK OlS^ THE [vol. Ixxvii, 



(d) The Calcareous-Soil Group. 



Considering that there was a Chalk outcrop in the upper reaches 

 of the Cam, comparatively close to Barnwell, it is not surprising 

 to find that the flora included plants o£ a definitelj^ calcicole type. 

 These were : — 



Thalictrum minus L. | f?) Liniim Prsecursor Reid. 



Papaver alpimim L. ' Dryas octopetala L. 



Arenaria gothica Fries. i Gentiana cruciata L. 



(?J Heliantliemum sp. ' 



The plants Ileliantliennim and Linum PrcBcursor are placed 

 here tentatively, for the recent species of Linum and Helian- 

 tliemum thrive best on a calcareous soil, and the unidentified 

 rock-rose and the extinct linseed may perhaps have shared this- 

 character. 



(e) The Estuarine Group. 



The presence of the following plants at Barnwell suggests tidal 

 influence : — 



Rumex maritimus L. j Eleochai^is uniglumis Link. 



Zannichellia pedunculata'ReiGhhevg. Garex arenaria L. (?). 

 Naias marina, var. intermedia A. Br. I Garex divisa Hudson. 



With the possible exception of ZannicJiellia pedunculata, no- 

 single plant in this list can be regarded as affording incontro- 

 vertible evidence of tidal influence; but, wdien we consider the group 

 as a whole, the marine tendenc}^ of all these plants does seem to 

 afford cumulative evidence of such a factor. The suggestion of 

 marine influence is not unreasonable, in view of the previous 

 history of the Fenland : for, even at the present time, a very small 

 estuarine flora still survives far inland in the county of Cambridge^ 

 and this element must have been larger before the comparatively 

 modern system of drains and sluices controlled the inflow of tidal 

 waters. 



It would appear, therefore, that the Barnwell Flora owed its 

 complexity to the admixture, in a single deposit, of leaves and 

 seeds from various parts of the river-basin. It included remains 

 of Arctic and Chalk plants which were transported some little 

 distance before they were incorporated in the peat-seams, and 

 were therefore usually represented by but few specimens except 

 in the case of the larger and tougher seeds. There w^ere also- 

 plants from the low-lying tract bordering the Fenland, w^here tidal 

 influence was probably felt. 



The facts here stated, which w^ere made apparent by the study 

 of a particular flora, have a bearing on the whole question of peats 

 in river-gravels. Considering that plants from several ecological 

 units must necessarily have been mixed together in any river- 

 gravel in which a flora is preserved, considerable variation between. 



