GEOGRAPHICAL VICISSITUDES OF PLANTS. 291 



of the compass. The Marsh Wood Spurge {Etiphorbia 

 pilosct), found in Somersetshire, is an outlying member 

 of the flora which existed here during the PHocene 

 Period, before the Irish Sea, the English Channel, 

 and the Bristol Channel had been formed, and when 

 the British Islands were a western extension of the 

 European continent. At that time one could have 

 wandered uninterruptedly from England to France and 

 Spain, for the land extended much farther into the 

 Atlantic than it does now. This Marsh Wood Spurge is 

 a common Mediterranean species. The Large-flowered 

 Butterwort {Pingiiiciila graitdiflora), found only in 

 Ireland, and the rarer Pale Butterwort {Pinginacla lusi- 

 tanica)^ met with only in a few places in the west of 

 England, are characteristic Spanish plants, as is also 

 the Fringed Rock Cress {Arabis ciliata) gathered near 

 the sea in the south of Ireland. The latter part of 

 the British Isles, as well as tracts in Devonshire, Corn- 

 wall, Somersetshire, etc., possess many similar plants, 

 whose characters are decidedly southern, and whose 

 headquarters are in the south of France, Spain, 

 Portugal, and along the Mediterranean coasts. It 

 was to account for these and other anomalous groups 

 of plants in our British flora that Professor Edward 

 Forbes, in his Geological Relations of the Fanna and 

 Flo7'a of the British Isles, thirty years ago suggested a 

 former land union between England and the Continent 

 by way of the English Channel ; and this brilliant 

 theory has since been verified in several ways, so that 



