14 BULLETIN OF THE NATURAL HISTOKY SOCIETY. 



a previous part of this address I have spoken of these zoo- 

 phites as growing upon the gulf weed that floats in the mid- 

 Atlantic, but they are found also in shallower water. 



The king-crabs and other modern crustaceans were repre- 

 sented in ancient times by the Trilobites, of which some 

 species were fitted for the deeper seas and others for shallow 

 waters. The trilobites were the most highly developed crus- 

 taceans of that early time. The Glass-sponge, which has been 

 spoken of as an inhabitant of deep still seas, had also its 

 representative in Cambrian times in the Protospongiae, 

 Cyathospongife, and other sponges with six- rayed spicules. 



The contrasted faunas or groups of animals of the warm 

 shallow seas and the deep cold seas in this part of the world, 

 lasted through a long period of time, so that throughout the 

 Cambrian and Ordovician ages there were along the Atlantic 

 coast of North America, as well as in many parts of Europe, 

 extensive tracts of cold sea water, more or less charged with 

 fine mud, that supported the second group of animals I have 

 spoken of ; and over the central parts of North America, and 

 subsequently in Europe, there were wide areas of the ocean, 

 shallow and warm ; here flourished the corals, nautiloid shells 

 and sea snails belonging to the flrst named or warm-water 

 fauna. 



Time, however, brought changes. The marginal areas of 

 the continent were elevated, and in the Silurian time the 

 cold-water faunas had but a precarious footing in many parts 

 of the eastern provinces of Canada. 



Both at the opening and close of Silurian time, if not 

 throughout its whole extent, lava-flows and discharges of 

 volcanic ashes occurred in various parts of Acadia, as pre- 

 liminary, perhaps, to the appearance above the water, of 

 large tracts of land which are found to have existed here in 

 the succeeding geological age — the Devonian. 



