LIFE IN THE EARLY CAMBRIAN 43 



hills bounding the St Lawrence River ; but for 

 the most part they have been swept away by the 

 sea when these districts were being elevated to form 

 parts of the American land. Their ruins appear as 

 boulders and pebbles in thick beds of conglomerate 

 or pudding-stone, constituting portions of the 

 Upper Cambrian and Lower Ordovician series, 

 which now occupy the south coast of the Lower 

 St. Lawrence. In one of these boulders, less than 

 a foot in diameter, removed from its hard matrix 

 and carefully broken up, I found fragments repre- 

 senting eleven different species, of which no less 

 than eight were trilobites, one a gastropod, one a 

 brachiopod, and one probably a sponge — and this 

 forms an interesting illustration of the number of 

 species sometimes to be found in a limited space, 

 and also of the great prevalence of the Trilobites 

 in these beds. The statistics of these groups for 

 North America, as given by Walcott, show 165 

 species belonging to all the groups enumerated 

 above, and of these the Trilobita constitute one-third 

 of the whole ; so that the Olenellus Zone, as it has 

 been called from one genus of these Crustaceans, 

 might well be named the reign of Trilobites, unless, 

 indeed, as the indications already referred to seem to 



