THE AGE OF THE WORLD. 571 



their formation that indicate an enormous lapse of time. The enormous depth 

 and vast extent of some of these formations, with certain attendant facts and 

 conditions, impress the mind almost with the force of a demonstration, that the 

 lapse of time during their formation must have been inconceivably great. Let us 

 begin with the Laurentian, the oldest fossil-bearing rock known to exist. These 

 are found to exist over a wide extent of country in both America and Europe. 

 They attain their greatest known development in Canada, where they exist to 

 the thickness of 40,000 feet. Supposing that they were formed by the gradual 

 detrition of older rocks, ?.nd the deposition of the debris at the bottom of the 

 ocean, the time required for the accumulation of such vast quantities of rock 

 material must have been very great. This fact seems further evident from the 

 presence in these rocks of certain substances that were accumulated in them 

 during their formation. Interstratified with the rocks, and sometimes existing 

 in pure beds, is found large quantities of graphite. This is doubtless the result 

 -of the perfect carbonization of vegetable matter. 



The growth of this vegetation would require long lapse of time, after which 

 it would probably pass slowly through the various grades of lignite, brown coal, 

 and anthracite, before reaching the stage of graphite. Another fact that seems 

 to demand the same interpretation in its relation to time, is the vast deposits of 

 iron ore during the Laurentian period. It is in the rocks of this period that we 

 find the rich iron beds of Missouri, New Jersey, Lake Superior, and Sweden. 

 This ore is supposed to have accumulated by the leaching of the oxides and car- 

 bonates of iron from the rocks, and its precipitation under the influence of de- 

 caying vegetation. 



Now if all the vast beds named above have been deposited by this process, 

 it must have consumed almost inconceivable time. The great Iron Mountain, of 

 Missouri, itself is estimated to contain not less than 600,000,000 tons of iron 

 above the level of the surrounding country. Extensive beds of limestone are 

 also found here; and as these are supposed to be composed of the shells of mol- 

 luscs and protozoans ; the time for them to live and die in quantities sufficient to 

 form such extensive beds of their calcareous remains, could scarcely be reckoned 

 in years. Next above these Eozoic rocks are the Silurian, aggregating a thick- 

 ness of over 25,000 feet, and crowded with fossils, both animal and vegetable. 

 More than 10,000 different species of fossil animals are already known to belong 

 to this system. These are not, as we would naturally expect from the age of the 

 rocks, of simple and primitive forms; but they are of widely differentiated and 

 highly specialized forms. Coming in as they do, suddenly, in such great variety, 

 and on such a high plane of organic life, how to account for their origin on the 

 hypothesis of evolution has been a very difficult problem. In order to surmou^it 

 the difficulty, believers in this doctrine generally take refuge in the assumption 

 that between the close of the Eozoic age, and the beginning of the Silurian age, 

 as represented in the rock of the two systems, there must have been an enormous 

 lapse of time, exceeding in extent all the time required for the formation of the 

 xocks composing both these systems. 



