THE MICROSCOPE IN MINERALOGY AND GEOLOGY. 93 



mends the maceration of the coal for about a week in a 

 solution of carbonate of potassium, when thin slices may 

 be cut with a razor. These should be gently heated in 

 nitric acid, and when they turn yellow, washed in cold 

 water and mounted in glycerin, as spirit and balsam ren- 

 der them opaque. Sometimes, as in anthracite, casts of 

 vegetable fibres may be obtained in the ash after burning 

 and mounted in balsam. 



The lignites of the tertiary period show a vegetable 

 structure similar to the woods of the present period, but 

 the older coal of the palaeozoic series is a mass of decom- 

 posed vegetable matter chiefly derived from the decay of 

 coniferous wood, analogous to the araucarise, as is seen 

 from the peculiar arrangement of the glandular dots on 

 the woody fibres. Traces of ferns, sigillarise, calarnites, 

 etc., such as are preserved in the shales and sandstones of 

 the coal period, are also met with, but their structure has 

 not been preserved. 



Professor Heer, of Zurich, has described and classified 

 several hundred species of fossil plants from the rniocene 

 beds of Switzerland by the outlines, nervation, and micro- 

 scopic structure of the leaves and character of sections of 

 the wood. Several hundred kinds of insects also have 

 been found in the same strata. It is remarkable that a 

 great part of this fossil flora is such as is now common 

 to America, as evergreen oaks, maples, poplars, ternate- 

 leaved pines, and the representatives of the gigantic 

 sequoise of California. 



The researches of palaeontologists have brought to light 

 nearly two thousand species of fossil plants, of which 

 about one-half belong to the carboniferous and one-fourth 

 to the tertiary formations. 



The rapid multiplication of the minute microscopic 

 organisms called diatoms, is such that Professor Ehren- 

 berg affirms it to have an important influence in blocking 

 up harbors and diminishing the depth of channels. These 



