TRACES OK THE GREAT ICE AGE IN DERBYSHIRE. 1 9 



in the vicinity, sometimes of rocks found in situ only at great 

 distances. The suggestions made from time to time that such 

 deposits are evidence of a deluge, or that they have been deposited 

 by water, cannot for one moment be entertained by those who have 

 studied them. Water possesses a wonderful capacity for sorting out 

 the material it transports, and depositing it in layers (depending 

 upon the character of the sediment and the velocity of the water) 

 in such a manner that it is impossible to confuse it with the 

 unstratified morainic matter which owes its position and arrange- 

 ment, or lack of arrangement, to ice. Besides this, the boulder- 

 clay is frequently found resting on rock surfaces which are 

 polished and grooved in a manner similar to those which are now 

 to be seen below existing glaciers, and in other cases it rests upon 

 strata which have been enormously disturbed and contorted as 

 by the passage of a glacier. 



Thick and widespread deposits, similar to our Ijoulder-clay, 

 occur upon the undulating low grounds of southern Sweden, Den- 

 mark, Holland, Switzerland, northern Germany, Poland, and Russia. 

 In Switzerland this material is known as " Moraine profonde " or 

 " Grundmordne" and as " Geschiebekhni" or " GeschiebeniergeV in 

 Germany. Often the boulders contained in it are striated and 

 polished in a manner impossible to be produced by any known 

 natural agent save ice, and in many cases the clay is crumpled 

 and exhibits a sort of lamination as though subjected to intense 

 pressure. 



Geologists recognise at least two of these boulder-clays, both 

 in these islands and on the continent of Europe, these being 

 separated in places by beds of terrestrial, freshwater, or marine 

 origin. In England, the lower boulder-clay has been traced as 

 far south as the valley of the Thames, while the upper one 

 does not extend south of the Midlands. These ittterglacial 

 beds (as the beds of aqueous origin separating the clays have 

 been called) indicate a retreat of the ice-sheet, and an ameliora- 

 tion of climatic conditions until the country was clothed with a 

 flora similar to that existing at the present day ; while animals 

 such as the wild ox, the great Irish deer, the horse, elephant and 



