ready for examination. Permanent slides are prepared by mounting the residue 

 in glycerine jelly. 



In macerating coals for plant microfossils, a different technique is followed. 

 The sample, after being broken into ± 1/2-inch fragments, is placed in a glass 

 beaker. Schultze's solution (saturated solution of 1 part potassium chlorate to 

 2 parts concentrated nitric acid) is added. After 12 hours under the hood, the 

 solution is diluted with distilled water and centrifuged; the liquid part is dis- 

 carded. The residue is then covered with ammonium hydroxide and allowed to 

 stand for approximately 2 minutes, after which time it is diluted with distilled 

 water and centrifuged. Washing is repeated several times. 



SUMMARY OF L.R.Wilson (1956) lists important microfos- 



IMPORTANT sils and separates them into three major di- 



MICROFOSSILS visions: (1) plant microfossils, (2) animal 



microfossils, and (3) microfossils of uncer- 

 tain affinity. For each group, Wilson includes type, description, geologic range, 

 habitat, size, and method of recovery. Wilson's sequence is followed in the en- 

 suing discussion. (See fig. 11-1.) 



Plant Microfossils 



Bacteria 



Probably the oldest known microfossils are bacteria. They have a geologic 

 range from the Algonkian to Recent. Although found in various rock types, in- 

 cluding oil shale, their value to the subsurface geologist is limited because of 

 their extremely small size and their uncertain ecological significance. Bacteria 

 are microscopic globose to rod-shaped, unicellular organisms found as isolated 

 cells or in chain-like arrangements. 



Coccolirhaceae (PI. 11-1, fig. 1} 



Little is known about the coccoliths (Coccolithaceae, Coccolithophoridae) . 

 These minute (2-15 microns) marine, planktonic forms have been assigned to 

 the algae by some workers and by others to the Protozoa. The living form in- 

 cludes a spherical cell whose walls are composed of small calcareous plates re- 

 ferred to as coccoliths. Classification of the coccoliths is based upon the mor- 

 phologic character of the plates, the most common being the perforate or imper- 

 forate disks. Although coccoliths have been reported in Upper Cambrian sedi- 

 ments, it was not until late Mesozoic that they became abundant. When better 

 understood, these comparatively unknown organisms may show promise of be- 

 coming important in biostratigraphic studies. 



207 



