INTRODUCTION. XXVU 



g'eolog'ists that the algee were among'st the first 

 vegetable productions which appeared during the 

 ancient Silurian epoch, they, along with a few shells 

 and Crustacea, are the earliest organized substances 

 met with in the fossiliferous rocks of that period. 

 In the Silurian limestone of North America entire 

 layers of rock are formed of a large digitate species 

 of fucus, named Fucoides Alleghaniensis 5 and in 

 Sweden, Kussia, and the Lake districts of England, 

 fucoids occur to the exclusion, so far as is yet 

 known, of every other vegetable form ; and such is 

 their abundance, in some localities, that they render 

 the argillaceous rocks, in which they lie diffused, 

 capable of being fired as an alum slate, and exist in 

 others as seams of a compact anthracite, occasionally 

 used as fuel. They also occur in those districts of 

 Wales in which the place and sequence of the 

 various Silurian formations were first determined, 

 though apparently in a state of keeping from which 

 little can be premised regarding their original forms. 

 During the Eed Sandstone period, from the abun- 

 dance of their remains, Hugh Miller tells us the sea 



