2 INFLUENCE OF CLIMATIC AND GEOLOGICAL CHANGES 



which flow into the western. He then sub-divided these 

 longitudinal portions transversely into provinces, or groups of 

 counties, which together constitute the basin of a principal 

 river. In this manner 18 provinces or groups of counties are 

 traced. Dorsetshire forms part of the Channel Province, and is 

 associated with Wilts, Hants, and Sussex. He separated also 

 the surface into six zones of heat, the boundary between the 

 third and fourth being the line of the practicable cultivation of 

 grain and potatoes, which is equal to the Arctic Circle at 

 sea-level. Very little of the actual surface of Britain falls on the 

 cold side of this line, because it is only mountain peaks that 

 overtop it. The late Professor E. Forbes separated the British 

 Islands into five sections, four of which he restricted to definite 

 provinces, and the fifth, besides claiming for it a large part of the 

 area, he overspreads and commingles with all the others. In 

 No. I. He includes the mountainous districts of the west and 

 south-west of Ireland, characterised by the presence of a few 

 species belonging to the families Saxifrageae, Ericaceae, 

 Lentibulariae, Cruciferae, besides other species, including Allium 

 Ampdoprasum a. Balingtonii, which grows wild in this county. 

 They are all natives of Northern Spain. This is his Lusitanian 

 type. No. II. This flora is found in the south-west and south- 

 east of Ireland, and includes a number of species not met with 

 elsewhere in the British Islands, but is intimately related to the 

 flora of the Channel Islands and the neighbouring part of 

 France, and marks a type of vegetation characteristic of Southern 

 Europe. A number of the plants are found associated with this 

 type in Cornwall and the Southern Counties, such as Oxalis cornicu- 

 latus, Lotus hispidus, Corrigiola littoralis, Polycarpon tetraphyllum, 

 Erica ciliaris, Cicendia filifomiis, Medicago denticulata, Rubia 

 peregrina. This is Watson's Atlantic type. No. III. Comprises 

 the south-east of England, where the British Cretaceous rocks 

 are chiefly developed, supporting a number of species, equally 

 common on the opposite coast of France. The entomology of 

 this part of England is influenced by, and in some cases is 

 dependent on, its flora. This forms part of Watson's Germanic 



