EECOKD OF LIFE IX THE ROCKS. 163 



could not be preserved at all, and the hard structures were 

 liable to be broken up or even destroyed, yet the rocks 

 abound in fossils. It is stated by Agassiz and Gould 

 that in most formations the number of species of animals 

 and plants found in any locality is not below that of the 

 species now living, in an area of equal extent and of a 

 similar character. For example, a coarse limestone in 

 the neighborhood of Paris contains not less than 1200 

 species of shells, more than twice the living species now 

 found in the Mediterranean. So, too, in a certain kind 

 of limestone in New York, called the Trenton limestone, 

 there have been found 170 species of shells, nearly as 

 many as are now found on the coast of Massachusetts. 

 The same is true of the individual plants and animals as 

 of their species. Extensive strata, as you have already 

 seen, are formed of the remains of animals, as corals and 

 shells, and the immense stores of coal are made up of the 

 remains of plants. Then there are the immense quanti- 

 ties of silicious fossils, for so they may be called, fur- 

 nished chiefly by those minute plants called diatoms, no- 

 ticed in 240. Of these the microscope shows us that 

 there is a great variety of species. 



247. Mode of Investigating Fossils. It is on the prin- 

 ciples of the science of comparative anatomy that the 

 fossils are investigated. This science may be said al- 

 most to have been founded by Cuvier, who acquired a 

 marvelous skill in prosecuting its researches. From a 

 few bones, sometimes even one small bone, of an un- 

 known animal, he could make out the construction of 

 the whole frame, and the character and habits of the an- 

 imal. The principles upon which this is done are very 

 simple. As in a machine each part has a relation to ev- 

 ery other part, so it is in the machinery of an animal ; 

 the relations in this case, however, being more perfect, 

 because the builder of the machine has perfect wisdom. 

 For example, teeth of a certain kind not only require a 

 certain kind of jaw, but a certain kind of feet also. An 



