TOPOGRAPHICAL REMARKS. XIX 



years becomes firm enough to bear the weight of a man, 

 although long affording a very treacherous footing. (See 

 " Sedgwick on the Geology of Cambridge," in Rep. Brit. 

 Assoc. 1845, Sections, p. 40, and "Jenyns on the Turf of 

 Cambridgeshire," in the same Report, p. 75. 



Formerly the natural produce of the unreclaimed Fen 

 land was cut, at intervals of two or three years, dried, 

 formed into bundles, and sold in the neighbouring towns 

 and villages for use in the lighting of fires, and for other 

 purposes. Within the last twenty years large quantities 

 were so used in our Colleges, but now its scarcity has caused 

 other materials to be employed. Then whole gangs of 

 barges loaded with sedge were often to be seen on the 

 Cam, arriving at this town ; now a single barge load is only 

 to be observed occasionally. 



In addition to these large districts of Chalk, Clay, and 

 Fen, there are three small and peculiar tracts to notice. At 

 the extreme west of the county the parish of Gamlingay 

 stands chiefly upon the Lower-green-sand Formation, and 

 included, until recently, a broad sandy heath, and extensive 

 quaking bogs. The enclosure of the Heath, and especially 

 the effectual drainage of the bogs, has been destructive to 

 some plants, although most 'of those which inhabited the 

 Heath may still be found. 



The following list contains the names of some of the plants 

 which are especially characteristic of the Gamlingay district. 



Teesdalia nudicaulis. Trifolium subterraneum. 



Moenchia erecta. Vicia sativa /? angustifolia. 



Sagina ciliata. Ornithopus perpusillus. 



Tilia parvifolia. Peplis portula. 



Genista anglica. Filago apiculata. 



