52 Botany 



flora, Nardiis stricta, Aira praecox, Anthoxanthum odoratum. Equally typical 

 of heath conditions are the mosses, Polytiichuiii piliferum, P. juiiiperintun, 

 Bryuiii rosciiiii, Dicramtiti scoparitnit var. orthophYlhiiii, Hypniim sthreberi, 

 Brachythecium albicans and. B.purmn. Until recently Tilia cordata and Quercus 

 sessilifiora apparently grew naturally here.' 



The Greensand outcrop at Ganilingay is also noteworthy because until 

 1855 it carried a large acidic peat bog yielding species quite characteristic 

 of the surfaces of raised bogs. The moors at Hinton, Teversham, and 

 Sawston, already mentioned, may have been more or less similar, but on a 

 large scale they are rare in the east of England. Peat investigations in the 

 Woodwalton and Yaxley areas of fen, south of Peterborough, show that 

 the peat fens locally passed into the condition of raised bogs, and that 

 limited marginal areas of fen surface retained this character and typical flora 

 until quite recent times. Most of the raised bog species from Gamlingay 

 are now extinct, but the records and herbarium specimens are sufficiently 

 convincing. They include the following : 



Hypericum elodes Lycopodimii chvattun 



Drosera rotuitdifolia L. inwidatmn 



Oxycoccus quadripetalus Spliagnum angustifolium 



Littorella laaistris S. mspidatum 



MaUxis paludosa Archidiiim alternijolium 



Narthecium ossifragum Splachnum ampuUaceum 



PotamogetOH polygoiiifolius Aulacoiniiiuin paUistre 



Scirpus paticijlortis Odontoschisma sphagiii 



Eriophorum angustifolium Aneura pinguis 



Ryiichospora alba Hyptnmi revolvens 



Carex dioica H. stellatum 



C. stellulata Philonotis Jontana 



Polytrichurn commune 



THE BOULDER CLAY 

 L Woodland 



The Boulder Clay in Cambridgesliire lies in two large patches, on the 

 eastern and western sides of the County (see Fig. 29). Place-name evidence 

 shows that these were the wooded districts of the County in the Anglo- 

 Saxon period.^ In Domesday times also, the distribution of woodland 

 varied sympathetically with that of the clay (see Fig. 17). To-day, by far 

 the greater part of the sparse woodland of the County is to be found in these 

 two areas. These woods are indeed almost the only semi-natural vegetation 



' Boulder Clay overlying Greensand in some places, and Gault in others, also occurs 

 at GamHngay, and supports woodland. See p. 54 below. 

 ' See p. 103 below. 



