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THE WONDERS OF GEOLOGY. Lect. VI. 



movements of the waters, and floating in the agitated me- 

 dium ; while others form immoveable rocks, which increase 

 slowly but surely, till they become elevated above the 

 surface of the waters, and constitute reefs and islands, as 

 I shall hereafter describe. 



The distribution of these animals is not solely regulated 

 by the relative depths of the water ; like plants, they vary 

 with the climate, and in cold latitudes the Cellariae and 

 Sertulariae, with a few Sponges and Alcyonia, are alone to 

 be met with. As we proceed to the 44th or 45th degree of 

 northern latitude, their number increases, and Gorgonise, 

 Sponges with loose tissue, and Millepores with foliated and 

 fragile expansions, appear in profusion. A little farther, 

 and the coral reddens the depths of the ocean with its 

 brilliant branches, and is soon followed by the large Madre- 

 pores. It is not, however, before the 34th degree of 

 northern latitude that the Corals become developed to the 

 grandeur and importance which they afterwards attain, to 

 the extent of a parallel southern latitude ; except in the 

 waters of the Atlantic, around the Bermuda Islands, where 

 corals abound, owing to the temperature induced by the 

 influence of the Gulf-stream. It is therefore within the 

 tropics, in a zone of more than 60 degrees expansion, that 

 these beings, scarcely visible to the naked eye, exercise 

 their empire, in a medium whose temperature knows no 

 change; and from the depths of the ocean elevate those 

 immense reefs, that may hereafter form a communication 

 between the inhabitants of the temperate zones.* I pro- 

 ceed to describe a few of the principal forms. 



16. The Sertularia, or vesicular coralline. — The 

 elegant arborescent Sertularia must be familiar to every 

 one who has rambled by the sea-side. This branch of the 

 Sea-pine coralline (Lign. 134), and which is shown mag- 

 nified in fig. 2, exhibits the usual appearance of these 

 * Lamouroux. 



