22 WORLD-MAKING 



the Norian rocks to be younger than the Lower Laurentian, and 

 that, as Logan supposed, considerable earth movements had 

 occurred between the two, implying lapse of time, while it is 

 also evident that the folding and crumpling of the Lower Lau- 

 rentian had led to great outbursts of igneous matter from below 

 the crust, or from its under part. 



Next to the Laurentian, but probably after an interval, the 

 rocks of which are yet scarcely known, we have the Huronian 

 of Logan, a series much less crystalline and more fragmentary, 

 and affording more evidence of land elevation and atmo- 

 spheric and aqueous erosion than those preceding it. It has 

 extensive beds of volcanic rock, great conglomerates, some of 

 them made up of rounded fragments of Laurentian rocks, and 

 others of quartz pebbles, which must have been the remains of 

 rocks subjected to very perfect decay. The pure quartz-rocks 

 tell the same tale, while slates and limestones speak also of 

 chemical separation of the materials of older rocks. The Hu- 

 ronian evidently tells of previous movements in the Lauren- 

 tian, and changes which allowed the Huronian to be deposited 

 along its shores and on the edges of its beds. Yet the Huronian 

 itself is older than the Palaeozoic series, and affected by power- 

 ful earth movements at an earlier date. Life existed in the 

 waters in Huronian times. We have spicules of sponges in 

 the limestone, and organic markings on the slaty beds ; but 

 they are few, and their nature is uncertain. 



Succeeding the Huronian, and made up of its debris and 

 that of the Laurentian, we have the great Cambrian series, 

 that in which we first find undoubted evidence of abundant 

 marine life, and which thus forms the first chapter in the great 

 Palaeozoic book of the early history of the world. Here let it 

 be observed we have at least two wide gaps in our history, 

 marked by the crumpling up, first, of the Laurentian, and then 

 of the Huronian beds. 



After what has been said, the reader will perhaps not be 



