THE DEVONIAN AGE. 91 



replaced by the siliceous or flinty matter in such a 

 manner that, when the surrounding limestone weathers 

 away, they remain projecting in relief in all the 

 beauty of their original forms. Not only so, but on 

 the surface of the country they remain as hard 

 siliceous stones, and may be found in ploughing the 

 soil and in stone fences and roadside heaps, so that 

 tons of them could often be collected over a very 

 limited space. When only partly disengaged from 

 the matrix, the process may be completed by im- 

 mersing them in a dilute acid. The beauty of these 

 specimens when thus prepared is very great not 

 at all inferior to that of modern corals, which they 

 often much resemble in general form, though dif- 

 fering in details of structure. One of the most 

 common forms is that of the Favosites, or honeycomb 

 coral, presenting regular hexagonal cells with trans- 

 verse floors or tabulae. Of these there are Severn,! 

 species, usually flat or massive in form; but one 

 species, F. polymorpha, branches out like the modern 

 stag-horn corals. Another curious form, Michelina, 

 looks exactly like a mass of the papery cells of the 

 great American hornet in a petrified state, and the 

 convex floors simulate the covers of the cells, so that 

 it is quite common to find them called fossil wasps'* 

 nests. Some of the largest belong to the genus 

 Philipsastrea or Smithia, which Hugh Miller has 

 immortalized by comparing its crowded stars, with 

 confluent rays, to the once-popular calico pattern 

 known as te Lane's net" a singular instance of tho 



