FAMILIES OF ROCKS 



trerae west, though these islands were destined to sink 

 again below the waves. Thence the ocean stretched 

 without a break, as at present, to Canada. A great 

 part of Canada's bleak lands was above the waters ; but 

 the United States, except for a few great islands, were 

 submerged. In the southern hemisphere South America, 

 split into numerous long reefs and islands, gave promise 

 of the continent to be; and there were great stretches 

 of land over Brazil, extending to the west where the 

 great chains of mountains now rise. Asia was largely 

 covered with shallow waters, and the whole extent of 

 the northern plains of Africa was sea. So far as we 

 are able to judge the distinctions of climates were less 

 marked then than now, and the conditions seem to 

 have been much more uniform over all the northern 

 hemisphere. This equality of climate lasted into the 

 next or Ordovician period. 



The Ordovician period glides insensibly into the Cam- 

 brian. There was no distinct break in the succession 

 of life. The species seem to have slowly extended and 

 developed from one of these great periods into another. 

 But the life of the Ordovician era, which has been 

 preserved for us, is much more abundant. Land was 

 beginning to emerge from the sea in greater bulk ; life 

 was springing up on the land and was emerging from 

 the sea, perhaps to take up its habitation there. The 

 first insect life appears in the Ordovician. It is not 

 an imposing relic except when seen through the eye 

 of imagination. It is just an obscure wing of an 

 insect which was found impressed on some shales found 



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