84 HIDDEN BEAUTIES OF NATURE 



creatures whose shells also form vast deposits in 

 certain parts of ocean floors, but which consist of 

 chalky or calcareous matter. These have been dealt 

 with in another chapter. 



The rock structure of the Tertiary period in 

 certain localities consists of marl, tripoli, and sand- 

 stones, composed mainly of the flinty skeletons and 

 shells of the polycystina family of Radiolaria. 



In another chapter two examples have been men- 

 tioned by way of illustration, namely the rocks of 

 the Barbados and those of the Nicobar Islands. The 

 former attain to a height of 1,100 feet, and the latter 

 to 2,000 feet in thickness. The microscopic rock- 

 making creatures of the world, at whatever period, 

 have never excelled in beauty or in complexity of 

 structure the fossil polycystina of the Barbadian 

 rocks. 



When exhibited under the microscope with proper 

 illumination, they constantly excite wonder and 

 admiration. 



These fossil shells that are so beautiful, notwith- 

 standing that they have been for ages pressed together 

 and consolidated into rocky strata hundreds of feet 

 in thickness and miles in extent, must have had at 

 one time living tenants, possessing power to take in 

 food and to appropriate flinty matter suspended in 

 the waters of an ocean that has many times over 

 been evaporated ! What a number of tremendous 

 problems at once confront us! If some millions of 

 these shells could be contained in a cubic inch of 



