THE PROGRESS OF LIFE 55 



the Mollusca and Trilobites of the Algonkian period 

 came into existence. 



ALGONKIAN LIFE 



In Nevada and Utah on the west, and in Vermont 

 and New Brunswick on the east of North America, as 

 also in North-west India, the Algonkian beds are over- 

 laid conformably by the Cambrian ; but in all other 

 known places, not only in North America, but also in 

 Europe, there is an unconformity at the base of the 

 Cambrian, thus distinctly separating the two systems. 



In the rocks of Animikie, near Lake Superior, a 

 shell something like Lingula, as well as some obscure 

 fragments of Trilobites and worm-like tracks have 

 been found. In the rocks of the Grand Canyon of 

 Colorado, where it passes through Arizona, Dr Walcott 

 has detected in a limestone, about 4000 feet below 

 the base of the Cambrian, abundant fragments of a 

 genus which differs from Stromatopora in having 

 thinner and coriaceous laminae without any connecting 

 pillars or pores. Four hundred and fifty feet higher 

 up he found a fragment of what seems to be the 

 pleural lobe of a segment of a Trilobite ; also a minute 

 discinoid or patelloid shell and a small Lingula-like 

 shell, possibly a Hyolithes. In North Vermont, at 

 about 500 feet below the base of the Cambrian, he 

 obtained fragments of a Trilobite and another so-called 

 Pteropod Salterella. In Conception Bay, Newfound- 

 land, a patelloid shell Aspidella terranovica and 

 worm tracks have been found in rocks underlying 

 uncomformably the Cambrian. And the Annelid (?) 

 tubes of the Torridon sandstone in north-west Scot- 



