XVI 



CONTENTS. 



PAGE 



Figure 6. Section of horizontal strata, 16 



Figure 7. Exposure of horizontal beds along the sides of a valley, ... 16 



Figure 8. Section showing the outcrop of tilted strata, 17 



Figure 9. Section of vertical beds, 17 



Figure 10. Section of folded beds, 17 



Figure 11. Section of horizontal beds, 18 



Figure 12. Horizontal beds with several layers exposed, 18 



Figure 13. Inclined strata, showing rise of the bed above sea level, ... 19 

 Figure 14. Outcrops of a clay bed on two sides of a hill and its prob- 

 able extension into same, 19 



Figure 15. Weathering penetrating a clay bed, 21 



Figure 16. Section showing weathered clay where the overburden is 



least, 22 



Figure 17. Occurrence of concretions in certain layers, 23 



Figure 18. Formation of spring due to ground water following a clay 



layer, 26 



Figure 19. Formation of a spring due to a layer of cemented sand, .... 26 

 Figure 20. Formation of a pond due to a clay bed underneath a de- 

 pression, 27 



Figure 21. Auger used for boring clay, 28 



Figure 22. Working clay by a tunnel, 31 



Figure 23. Mining clay by a shaft, 31 



Figure 24. Pit working of Middlesex district, 33 



Figure 25. Curve showing effect of titanium oxide on fusibility of 



clay, 71 



Figure 26. Briquette for testing the tensile strength of clay, 84 



Figure 27. Curves showing relation of texture to tensile strength, .... 89 



Figure 30. Drawing showing particles of a Cape May clay, 109 



Figure 31. Drawing showing particles of an Alloway clay, no 



Figure 32. Drawing showing grains of sand in a Clay Marl I, in 



Figure 33. Grains of fine and medium sand of Clay Marl I, 112 



Figure 34. Particles of Clay Marl I, 113 



Figure 35. Erosion of a clay layer before the glacial drift was de- 

 posited, 187 



Figure 36. Erosion along a valley through several clay beds, 188 



Figure 37. Method of testing the breaking strength of brick, ......... 252 



Figure 38. Diagram showing relation of crushing strength to trans- 

 verse strength of a soft-mud brick, 257 



Figure 39. Diagram showing relation of crushing strength to trans- 

 verse strength of stiff-mud brick, 258 



Figure 40. Diagram showing effect of silica on the fusion point when 



mixed with alumina and kaolin, 313 



Figure 41. Diagram showing effects of silica and titanium on the fusi- 

 bility of kaolin, 314 



