74 J. A. UDDEN 



in one instance slightly dissolved away. The tubular impreg- 

 nations in the stony layers of the formation appear to be marked 

 off from the mass of the rock so as to sometimes weather out 

 like casts of fucoid stems. In other instances they appear like 

 slightly more colored parts of the rock. The thread-like exten- 

 sions of green clay which form a network in the dark shale at 

 some horizons where it comes in contact with the lighter shale 

 vary in coarseness at different places. There is nothing to indi- 

 cate a structural boundary between the green in the threads and 

 their dark matrix, and there is hardly anything to suggest that 

 they have an organic origin. It seems more likely that they 

 have resulted from some progressive change in the mineral 

 nature of the shale. Excepting the lingulas, the fossils which 

 occur in the layer numbered 6 in the general section are all of a 

 black and bituminous substance, which is apt to break and fall 

 out in drying, leaving only a mold. The dark shale in numbers 

 6 and 7 is fine and very uniform in character. Occasionally 

 it is difficult to distinguish from the Coal Measure shale, but 

 the latter usually contains small mica scales, which are absent 

 from the former. Where not weathered, these beds contain a 

 considerable amount of bituminous material, which on distillation 

 yields inflammable gas and oil. The several layers of the 

 formation have been examined for phosphate by Dr. j. B. 

 Weems, who finds 2.01 per cent, in number 7, 1.94 per cent, in 

 number 6, 2.09 and 2.18 per cent, respectively in two analyses of 

 material from number 5, 3.18 per cent, in number 4, 6.82 and 

 5.29 per cent, respectively in two analyses of material from 

 number 3, 5.43 per cent, in number 2, and 4.86 per cent, in 

 number 1. 



Structural Relations. — As already shown, a pronounced uncon- 

 formity separates this formation from the overlying Coal Meas- 

 ures. The erosion interval preceding the deposition of the 

 latter has left its marks, not only in the reliefs which extend 

 from the top of these beds to a considerable distance below 

 their base into the underlying limestone, but also in the weath- 

 ering of the Sweetland Creek beds, especially where these rise 



