94 The Microscope. 



extensive stratum of earth, which, when examined 

 with the microscope, turns out to be entirely com- 

 posed of fossilized diatoms, he feels no doubt that it 

 has once been the bottom of a lake or sea. 



And there are minute animals which give similar 

 evidence with respect to the great chalk formation, 

 and to the limestone rock which forms so considerable 

 a portion of the earth's crust. 



As I write, a slide is placed on the microscope 

 stage, containing a little mud apparently, obtained 

 some years ago by deep-sea soundings from the bed 

 of the Atlantic Ocean, one thousand eight hundred 

 and thirty fathoms deep, to wit, more than two miles. I 

 view it with a magnifying power of twenty diameters, 

 and see that it consists of a multitude of minute nau- 

 tilus-like shells, some broken, some perfect, and of 

 several shapeless fragments. These little shells are 

 not of the nautilus species, their inmates having been 

 discovered to be widely different from those of the 

 nautilus shell. They are of the very numerous class 

 designated Foraminifera, and Dr. Carpenter states 

 that they are found living on the upper surface of the 

 " ooze " forming the bed of the Atlantic, while its 

 lower layers are almost entirely composed of dead 

 shells of the same type. 



A section of limestone will be found to present an 

 appearance somewhat similar to that of the ooze of 

 the Atlantic ; for all limestone is composed of a mass 

 of extremely minute animal remains, among which the 

 Foraminifera abound, as also in chalk. It is not very 

 difficult to make a section of limestone. A small thin 



