170 PROGRESS OF SCIENCE. 



computed that for the deposit of the Rhine Valley loess 

 alone, 320,000 years must have been necessary ; but taking 

 the minimum estimate, we may boldly say that the Glacial 

 era cannot have begun less than 300,000 years ago. The 

 point is of importance because it bears upon the antiquity, 

 not of the earth only, since the Glacial epoch is a mere 

 fraction of the earth's life, but upon the antiquity of the 

 human race, for there is evidence that man existed through- 

 out the Ice Age, and probably long before, that is, in the 

 Tertiary period ; many of the palseontological implements 

 in our possession are clearly the handicraft of pre-Glacial 

 man, for they were found in pre-Glacial deposits. 



The brief survey of geology enables us to measure the 

 work performed by modern inquirers in a new field. Two 

 centuries ago mankind was in total ignorance of the earth's 

 history. A few valuable hints had been given by Avicenna, 

 by Leonardo, by Palissy, but they were too slight on the 

 whole to awaken anything beyond curiosity or doubt. The 

 modern era opens a new expanse, where guesses are taken as 

 of no account, and are replaced by ceaseless observation 

 which conduces to substantial knowledge. The first tentative 

 steps are in the right direction and lead at once to creditable 

 results, but the march, gradual and somewhat wayward in 

 the beginning, in time becomes steady, then becomes rapid, 

 and conducts the stout explorers, despite strong barriers and 

 frequent obscurity, to victorious achievements. Patient 

 labour has disclosed the history of the world we live in. 

 Vast regions are as yet virgin soil to the geologist; large 

 tracts in Asia, in Africa, are yet unexplored ; but the areas 

 which have been visited and probed are so varied, so nume- 

 rous, and so distant from, or so close to, one another, that we 

 may proclaim geology a triumphant science all along the 

 line, for it has now accomplished its work the facts as yet 

 unravelled are relatively mere details. Murchison's labours 

 alone would enable us to describe the growth and the con- 

 stitution of the earth with almost absolute certainty, so widely 

 did they extend, and so conscientiously were they carried 

 out. But geology does not show us the structure of the 

 earth only ; it also teaches us great truths that were not so 



