THE SUB-TROPICAL ZONE. 173 



A very interesting circumstance connected with these 

 Zamias must just be mentioned, which, like the fossil-trees 

 at the North Pole, proves that our globe at some previous 

 time had a very different constitution from its present one. 

 Though Zamias are only found at the present day in the 

 warm climate of South Africa, of tropical South America, and 

 the north of New Holland, there are nevertheless numbers of 

 fossils found imbedded in the building-stone of the Isle of 

 Portland, which Dr. Buckland identified with the under- 

 ground part of the stem of these trees, and which, even to 

 the eye of a common observer, bear a striking resemblance 

 to the stem of the species called Encephalartos horridus. 

 These fossils commonly go by the name of petrified birds'- 

 nests. 



A striking character is given to vegetation at the Cape 

 of Good Hope by the great prevalence of the Heath tribe 

 (Ericas), which here reaches its greatest development. We 

 have indeed in the Northern Hemisphere single representa- 

 tives of the family, which have a very wide range, extending 

 northwards as far as Kamtschatka, and even into the Arctic 

 Zone, to Lapland and Greenland ; and in a southerly direc- 

 tion we find them assuming even an arborescent appearance, 

 in the extreme South of Europe, that is to say, and in the 



