FIGURES (Continued) 



Page 



4o Drilling Crew Disconnecting Pull Piece 7 



5. Cathead Acting as a Rope Clutch 8 



6. Diagram of Drill Rig , . . . . 9 



7. Washbit 10 



8. Two Common Samplers and Some Sample Retainers 12 



9. Geospace GT-2A Portable Refraction System 15 



10. Geophone in Soil » ..o ............ . 16 



11. Type 47 Polaroid Film Record . , 17 



12. Diagram of Seismic Profile Layout 18 



13. Offset Distance and Critical Angle 21 



14. Apparent and True Bedrock Velocities . 23 



15. Determination of Bedrock Relief by AT 24 



16. Example of a Non-Zero Intercept 26 



17. Apparent Sediment Velocities Due to Variable 



Thickness 27 



18. Time-Distance Plot Showing a Time Step for Buried 



Peat 28 



19. Profile from PI-7 and Drill Hole PIC 29 



20. Time-Distance Plot and Cross Section from PI-17 31 



21. Time-Distance Plot from Middle Ground 32 



22. Cross Section of Middle Ground Showing 



a Bedrock High 33 



23. Graphical Explanation of the "Blind Zone" , 35 



24. Nomogram for "Blind-Zone" Computation. . 36 



25. Transverse Profiles Showing a Bedrock Rise 38 



V i 



