XVIII LIST OF ILLUSTRATIONS. 
27. Porites with linear cavities from the removal of crystals. 91 
28. Undulation and thickening of strata. 92 
29. Concretionary structure in Niagara limestone. 93 
30. Curved or concretionary strata — View of Porter’s quarry, Niagara falls. ........ 94 
31. Similar structure to the above, from the Third district. 94 
32. Lignilites, or Magnesian striae. 95 
33. Fossils of the Niagara group. 101 
34. Ditto . 103 
35. Ditto . 104 
36. Ditto . 105 
37 and 38. Ditto . 108 
39. Ditto . 109 
40. Ditto 110 
41. Ditto . 112 
41 (read 41 bis). Ditto . 113 
42. Ditto 115 
43. Ditto 116 
44. Section illustrating the order among the strata forming the Onondaga salt group.... 119 
45. Section of a gypsum quarry... 121 
46. Section on the bank of the Canandaigua outlet; gypsum quarries. 122 
47 and 48. Gypsum quarries. 123 
49. Ditto . 125 
50. Pseudomorphous hopper-shaped crystals. 127 
51. Porous or vermicular limestone..... 128 
52. Lignilites, or epsomites . .. 130 
53. Vertical suture of the same... 131 
54. Fossils of the Onondaga salt group... 137 
55 and 56. Sections showing the order of superposition. 139 
57. Water-limestone with linear cavities. 142 
58. Fossils of the Water-lime group. 142 
59. Fossils of the Oriskany sandstone. 148 
60. Ditto 149 
61. Fossils of the Onondaga limestone. 157 
62. Ditto 159 
63. Ditto 160 
64. View of a quarry in the Corniferous limestone. 161 
65. Sections showing supposed faults of strata in the Corniferous limestone.. 163 
66 . Sections showing fissures in the Corniferous limestone. 169 
67. Fossils of the Corniferous limestone. 171 
68 . Ditto 172 
69. Ichthyodorulite. 174 
70. Fossils of the Corniferous limestone. 175 
71. Fossils of the Marcellus shale . ...... ..... 180 
