GEOLOGY OF THE BEISTOL COAL-FIELD. 



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5. — [433]. — Fenestella led. This is light coloured limestone 

 about 1 foot thick, containing plenty of good specimens of Fenestella 

 Jldbellata and other Bryozoa. 



6. — [448] . — Bryozoa led. This very remarkable deposit is 8 feet 

 thick, of dark red siliceous rock mixed with crystalline limestone. 

 It is one mass of minute casts of fossils in a compound of silica and 

 ferric oxide. They being insoluble in tolerably strong Hydrochloric 

 acid may be easily separated from the lime. A very favorite 

 method of preparing specimens is to suspend a piece of the rock in 

 a beaker of acid till a portion has been dissolved, then removed and 

 dried. The fossils then appear all over the surface, standing out in 

 the most beautiful manner. On gently washing the sediment in 

 the beaker plenty of loose fossils may be obtained ready for the 

 microscope. To give an idea of the immense number of organisms 

 present in the rock, more than one million and a half have been 



