12 THE DAWN OF LIFE. 



are, however, already extensively settled, and the 

 traveller may pass through a succession of more 

 or less cultivated valleys, bounded by rocks or 

 wooded hills and crags, and diversified by running 

 streams and romantic lakes and ponds, constituting 

 a country always picturesque and often beautiful, 

 and rearing a strong and hardy population. To the 

 geologist it presents in the main immensely thick 

 beds of gneiss, and similar metamorphic and crystal- 

 line rocks, contorted in the most remarkable manner, 

 so that if they could be flattened out they would serve 

 as a skin much too large** for mother earth in her 

 present state, so much has she shrunk and wrinkled 

 since those youthful days when the Laurentian rocks 

 were her outer covering. (Fig. 3.) 



The elaborate sections of Sir William Logan show 

 that these old rocks are divisible into two series, the 

 Lower and Upper Laurentian; the latter being the 

 newer of the two, and perhaps separated from, the 

 former by a long interval of time ; but this Upper 

 Laurentian being probably itself older than the 

 Huronian series, and this again older than all ^ the 

 other stratified rocks. The Lower Laurentian, which 

 attains to a thickness of more than 20,000 feet, con- 

 sists of stratified granitic rocks or gneisses, of indu- 

 rated sandstone or quartzite, of mica and hornblende 

 schist, and of crystalline limestones or marbles, and 

 iron ores, the whole interstratified with each other. 

 The Upper Laurentian, which is 10,000 feet thick at 

 least, consists in part of similar rocks, but associated 



