58 NOTES ON THE FLORA OF LINCOLNSHIRE. 



Of interesting varieties we have Sonchus arvensis L. glabra, an 

 absolutely glabrous form. "It quite simulates S. maritimus," as 

 Mr. Bennett says. In County and Bennett Herbaria. 



No one need attempt to solve the mysteries of plant distribution 

 in Lincolnshire without some knowledge of our recent geological 

 changes. The artificial boundary chosen by Watson for the N. 

 and S. vice-counties, the river Witham from the Wash to Lincoln 

 and the Fossdyke from that city to the spot where it touches the 

 border of Nottingham, is a great natural boundary which existed 

 before the Ice Age. The boulder clay outcropping from below the 

 recent river gravel deposits of the Trent valley proves that it changed 

 its course in late geological times. The line of its ancient gravels 

 prove it to have flowed along the present course of the Witham 

 from Lincoln. Yet it can hardly be supposed to have definitely 

 taken its present course till historical times, as even now it has to 

 be prevented from passing ofi:' some part of its flood-water through 

 the Lincoln gap and along the Witham channel by a bank at 

 Spalford in Notts. The wide gap cut by water in the limestone 

 hill at Lincoln proves the width and power of the ancient stream 

 that flowed unembanked as the boundary between the N. and S. vice- 

 counties. At some time previous to the great ice age too, the 

 whole of the cretaceous strata and the Kimeridge clay of the upper 

 oolite were denuded down to the Oxford clay of the middle oolite 

 throughout the great Lincolnshire fenland. The recent deposits 

 lying on this Oxford clay floor, in order from the lowest upward, 

 are boulder clay, gravelly sand, ancient peat, a.lluvium, and, in a 

 few stops in N., modern peat. The soils of the grea,t fenland are 

 silt with a fringe of old peat as the land rises to the upper ground. 

 The sea-coast of N., from the mouth of the Humber to that of the 

 Wash, are fringed with blown sea-washed sands where silt is not 

 deposited. There is no such sand-band in S. As soon as the shore 

 is banked up with sand silt brought down by the fen rivers is 

 deposited by the spring tides, and the "fifty" or saltmarsh flora 

 is the result in S. ; and at the mouth of the Humber, and along 

 the northern shore of the Wash in N. 



Sandy-shore species found in N. for which there is no proper 

 habitat in S.: — Thalictrum. dimense ; Ranimciiliis Baudotii and varie- 

 ties — sand-loving, I suppose, or I cannot understand its absence 

 from S. ; Glaucium JJavum, an erratic uncertain species with us ; 

 Cakile maritima, Cerastkim tetrandum, Sagina maritima, Lathyrus 

 luanthmis, Eryngiiim maritimum ; Senecio vlscosiis, confined to a 

 very limited area on the sand-band, — a new introduction perhaps ; 

 Knjthraa pulchella, Volvulus Soldanella, Atriplex lacinata, Salsola, 

 Hippopliae, FAiphorhia portlandica, confined to one stop; Ammophila 

 arnndmacea, Festuca arenaria, and Elymus arenarins. 



Peat fen species found in N., for which there never was much 

 habitat, and now is practically none in S. : — Lathyrus pahi'itris, 

 Drosera anglica, D. internieclia, Peucedanum p)(ilustre, Se7iecio paliistris, 

 Sonchus palustris, Potamogeton color atus, Cladium jamaicense, and 

 Lastraa Thelypteris. 



Moorland and moorland pool-loving species, which cannot 



