94 MICROSCOPIC OBJECTS, 



thick, are by far the most interesting for the microscope. 

 Some specimens are beheved to be sihcified sponge ; 

 indeed remains have been seen so perfect as to admit of 

 identification and naming, as the Dysidia fragilis. The 

 intense red colour of the fossilized parts, and the trans- 

 parency of the colourless portions, (which latter affect 

 polarized light), are well seen under apower of 40 diameters. 



Moss Agate. — ^Thin sections of this substance afford 

 interesting subjects for the microscope. The green earthy 

 matter Chlorite is often diffused through it in such a 

 manner as to resemble moss, and was supposed to be 

 vegetable matter imbedded within it. In some speci- 

 mens, parts of the sihca take the structure of calce- 

 dony ; these specimens should be viewed by polarized 

 hght. 



Oolites. — Rocks are separable into two grand divi- 

 sions, the CrystaUized and the Stratified : the former (of 

 which granite may be taken as an example) is the primi- 

 tive formation, and must have been produced at a very 

 high temperature. It varies greatly in hardness and 

 durability : this arises from differences in the aggregation 

 of the silica, felspar, and mica of which it is composed. 

 In general, the most compact is that in which the plates 

 of mica are smallest. This kind, however, which in 

 other respects would be so desirable for building pur- 

 poses, is so hard that the time and expense required in 

 working it preclude its application to such uses. For the 

 microscope a series of specimens from different quarries 

 would be a valuable addition to a cabinet. There should 



