THE CHALK PERIOD 



part of what is now the Western Mediterranean), and 

 most of Turkey and Hungary. But elsewhere marine 

 animals succeeded the reptiles, and the foundations of 

 all the chalk hills and cliffs of modern Europe were laid. 



Of what were they made ? We may borrow a capital 

 suggestion from Mr. Jerome Harrison, of Birmingham 

 University. "Take," he says, "a piece of chalk and 

 brush it vigorously with a tooth-brush in a glass of water 

 until the liquid looks quite milky. Allow the greater 

 part of the sediment to subside, and then pour away the 

 water and wash the material which has sunk to the 

 bottom of the glass by pouring water on it two or three 

 times. Put the whitish powder which finally remains 

 under a microscope ; and examine it with, say, the 

 quarter-inch power, which will magnify about 300 diam- 

 eters. The greater part of the white powder will 

 then be seen to be composed of the minute shells of 

 creatures called Foraminifera little specks of jelly-like 

 matter which secrete for themselves a shell or covering 

 from the carbonate of lime dissolved in the sea-water in 

 which they live. 



" Countless millions of foraminifera inhabit the waters 

 of the North Atlantic (and of other deep seas) at the 

 present day ; and of these at least one species Globigerina 

 bullo'ides cannot be distinguished from one of the com- 

 monest species found in the White Chalk. When these 

 tiny animals die their soft parts soon decay and dis- 

 appear, and their skeletons (or shells) fall on the sea floor, 

 where they form a whitish mud or 'ooze/ The time 

 required for the accumulation of so thick a deposit com- 



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