342 Subsurface Geologic Methods 



concerned only with the study of microfaunas? Why? 



11. How is detrital mineralogy helpful in establishing subsurface corre- 

 lations? 



12. How are rotary well samples obtained? 



13. What is the difference in quality of a rotary and a cable-tool well 

 sample? 



14. What are the chief disadvantages of coring? 



15. What major characteristics of a rock should be observed during 

 binocular examination? 



16. Define porosity, permeability, texture, structure. 



17. Hills recommends two principal procedures for describing well cut- 

 tings. What are they? 



18. What is meant by "heavy minerals" in sedimentary deposits? Name 

 several common heavy minerals. 



19. Briefly outline the procedure for preparing heavy mineral fraction- 

 ates? 



20. How is heavy-mineral data used in correlation work? 



21. What is the difference between the "roundness" and "sphericity" of 

 a sand grain? 



22. What are the advantages of studying detrital minerals in thin section? 



23. Define "insoluble residue." How are such residues prepared? 



24. What materials constitute the more common "insolubles" ? 



25. Define: dolomold, drusy, euhedral, oolith, granulated, spicular, and 

 subhedral. 



26. What are the primary means for differentiating various cherts? 



27. How are insoluble residues used in correlation work? 



28. A method of plotting insoluble-residue data is shown in figures 58 

 and 59. Study. 



29. What procedure is followed in preparing a thin section of friable 

 material ? 



30. Define petrofabrics. 



31. Give a map symbol for: plunging syncline, reverse fault, concealed 

 anticline, overturned anticline. 



32. What procedure is followed in collecting a sample in the field for 

 petrofabric study? 



33. What are the applications of petrofabric studies? 



34. How may size analysis be applied in stratigraphic investigations? 



35. What is a histogram, simple-frequency curve, and cumulative-fre- 

 quency curve? 



36. How is the coefficient of sorting of a sediment determined, and what 

 is the significance of this value? 



37. What staining methods are used for distinguishing calcite from 



38. Outline the procedure for preparing a clay sample for stain anlysis. 



