96 THE MICROSCOPIST. 



by the deep-sea soundings made preparatory to laying 

 the telegraph cable across the Atlantic Ocean. Professor 

 Huxley found the mud composing the floor of the ocean 

 to consist of minute Rhizopods or Foraminifera, of the 

 genus Globigerina, together with Polycystina and Dia- 

 toms, and a few siliceous spiculse of sponges. These were 

 connected by a mass of living gelatinous matter, to which 

 he has given the name of Bathybius, and which contains 

 minute bodies termed Coccoliths and Coccospheres, which 

 have also been detected in fossil chalk. It is said that 

 95 per cent, of the mud of the North Atlantic consists of 

 Globigerina shells. 



To examine Foraminifera in chalk, rub a quantity to 

 powder in water with a soft brush, and let it settle for a 

 variable time. The first deposits will contain the larger 

 specimens, with fragments of shell, etc. ; the smaller fall 

 next, while the amorphous particles suspended in the 

 water may be cast aside. After drying such specimens 

 as may be selected by the use of a dissecting microscope 

 or Coddington lens, etc., they may be mounted in balsam. 



The flint found in chalk often contains Xanthidia, 

 which are the sporangia of Desmidiacese, as well as speci- 

 mens of sponge, Foraminiferal shells, etc. They must be 

 cut as other hard minerals. 



There are other deposits besides chalk which are seen 

 by the microscope to consist of minute shells, corals, 

 etc. A section of oolitic stone will often show that each 

 rounded concretion is composed of a series of concentric 

 spheres inclosing a central nucleus which may be a forami- 

 niferal shell. The green sand formation is composed of 

 the casts of the interior of minute shells which have them- 

 selves entirely disappeared. The material of these casts, 

 chiefly silex colored with iron, has not only filled the cham- 

 bers of the shells, but has penetrated the canals of the 

 intermediate skeleton. 



The more recent discovery by Drs. Dawson and Carpen- 



