204 A LUMP OF CHALK AND ITS LESSONS. 



to notice the appearance of a number of small grains of a 

 greenish. coloured mineral. If, again, we try to dissolve 

 this lower chalk in acid we shall find that as we descend 

 in the series there is an ever-increasing quantity of an 

 insoluble remnant, which would be shown by analysis to be 

 of the nature of clay. Both these circumstances point to 

 the conclusion that at the time the lower chalk was laid 

 down the conditions were by no means so well adapted for 

 the deposition of a pure carbonate of lime as was the case 

 in the later time of the upper chalk with flints. What 

 these conditions were we shall consider subsequently, but 

 we have now to direct our attention to the area over which 

 the white chalk extends. 



In the north-west the furthest limits to which the white 

 chalk extended are found near Belfast, where, as we have 

 said, the rock has been converted into a hard limestone by 

 the action of heat. Although we do not again meet with 

 chalk till we reach the east and south of England, where 

 it forms large portions of our coast from Dorsetshire to 

 Yorkshire, yet it is probable that the chalk sea embraced 

 the foot of the Welsh mountains, which formed an 

 archipelago. From England the white chalk may be 

 traced without any alteration in its character through the 

 north of France, the south of Belgium, the eastern part of 

 the Netherlands, and thence through Westphalia, Hanover, 

 and Galicia, into Poland and Russia, where it reaches on 

 the one side to the foot of the Urals, and on the other to the 

 Crimea ; moreover, to the northward it occupies a con- 

 siderable portion of Denmark and the southern extremity of 

 Sweden. Although the white chalk is now only distributed 

 over the surface of this region in larger or smaller patches, 

 being sometimes covered up by newer (Tertiary) deposits, 

 and in other places totally wanting, there is evidence that 

 it once extended continuously over the whole. Moreover, 

 the absence of any traces of the white chalk in the regions 

 to the west and north of those mentioned, indicates that 

 the present limits of the chalk in those directions mark 

 approximately the boundaries of this cretaceous sea, this 

 sea being probably cut off from free communication 

 with the Atlantic by a barrier connecting western France 



