THE LESSONS OF A QUARRY. 215 



By-and-by there come changes of land-surface. 

 There may be sinking, or there may be upheaval. In 

 any case, the old river-course becomes altered, and 

 the filled-up lake-basin is seen to form part and parcel 

 of the solid land. Its materials have been consolidated 

 and massed together, and for long ages it lies buried 

 and unheeded in the earth's crust. Then man arrives 

 with his prying demand for building stone. He fer- 

 rets out the presence of rock below the site of the 

 old lake-bed, and soon the superficial debris is cleared 

 away, and the strata of rock below are laid bare. 



For the river-material has become rock, and it 

 has arranged itself in layers or strata, because of the 

 regularity of its deposition in the water. The " wear 

 and tear " of a former state of things have become the 

 rocks of to-day ; just as the river-worn substances now 

 being hurried into lake and sea will become the strati- 

 fied rocks of the future. Our quarry is part and 

 parcel of an old filled-up lake-bed ; and we know this, 

 because, in the words of geology, " the present is the 

 key to the past ; " and because the history of our 

 world may be read and written on the same lines as 

 those whereon the story of the quarry is made plain. 

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