1818.] Scfentifc Intelligence. 469 



feet long, of a bright yellow, and sometimes of a blue colour ; 

 same resemble snails, and some are not unlike lobsters in shape, 

 but soft, and not above two inches long. 



The growth of coral appears to cease when the worm is no 

 longer exposed to the washing of the sea. Thus, a reef rises in 

 the form of a cauliflower, till its top has gained the level of the 

 highest tides, above which the worm has no power to advance, 

 and the reef of course no longer extends itself upwards. The 

 other parts, in succession, reach the surface, and there stop, 

 forming in time a level field with steep sides all round. The 

 reef, however, continually increases ; and being prevented from 

 going higher, extends itself laterally in all directions. But this 

 growth being as rapid at the upper edge as it is lower down, the 

 steepness of the face of the r^ef is still preserved.. These are 

 the circumstances which render coral reefs so dangerous in 

 navigation ; fir, in the first place, they are seldom seen above 

 the water, and, in the next, their sides are so steep that a ship's 

 bows may strike against the rock before any change of sound- 

 ings has given warning of the danger. 



XI. Account of a new Mineral called Pargasite* 



A new mineral called pargasite has been sent to this country 

 from Finland. It was found some years ago at the village of 

 Ersby, near Abo. 



it is of a green colour, is translucent, and transparent. Its 

 crystals are of various sizes, from an inch downwards. Its form 

 is an octohedron, with a rhomboidal base. It has three cleavages. 

 It is harder than fluor spar, but is scratched by quartz. It also 

 scratches glass. Specific gravity 3-11. It melts before the 

 blow-pipe into a mass of a pearly white lustre. The following 

 are given as the proportions of its constituents : 



Silex 42-01 



Magnesia 18-27 



Lime 14-28 



Alumina ■ 14-08 



Oxide of iron o'O 



Oxide of manganese 1'02 



Oxide of a metal not investigated - 33 



Fluoric acid and water 3*09 



Loss 2-59 



100-00 



XII. Lectures. 

 Dr. Bostock proposes to give a Course of Lectures o i Phy- 



logy and Animal Chemistry during the next winter. 



* Extracted from the Journal of Science and the Arts, v. 1-8 



