120 LIFE ON THE EARTH. 



countenancing speculations which assign to the hu- 

 man race a period very much longer than that 

 hitherto adopted on historical grounds. They de- 

 serve no rebuke, however, for the endeavour to force 

 their way into the citadel of natural truth, if they 

 undertake the siege after a sufficient survey of the 

 difficulties of the enterprise, which in this case are 

 not slight. Let any one acquainted with the modern 

 aspect of Astronomy, consider well the nature of 

 that problem which, omitting all previous cosmical 

 changes, would count the years since the planet be- 

 came a terraqueous globe let him then look at the 

 Mosaic narrative, and be satisfied with the truth, 

 that 'In the beginning God created the heavens 

 and the Earth,' for no measures of time conceivable 

 by man will reach back to that remote epoch in the 

 history of our solar system. That, however, is the 

 starting-point of physical geography, for then began 

 the movements and changes in land, water, and air, 

 which it is the business of geology to register and in- 

 terpret. As already explained, the gift of life on this 

 earth is limited by conditions within which alone it is 

 possible: until these conditions were attained that 

 is to say, arrived at in the pre-ordained course of 

 nature the earth might be well described by the 

 words ' without form, and void.' For the rocky mo- 

 numents of this period, which we have endeavoured 



