162 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



Peat deposits rest as do coal beds on sandstone, shale, clay or 

 limestone and the limestone may be either fresh water or marine. 

 Like coal beds they underlie a roof of any sort and at times they are 

 intercalations in marine calcareous shales. The association with 

 marine beds is clearly no evidence of deep water or of flexibility in 

 the earth's crust. 



In Conclusion. 



The coal beds and the associated rocks are of land origin ; the 

 detrital deposits are those made by flooding waters on wide-spread- 

 ing plains ; the coal beds, in all essential features, bear remarkable 

 resemblance to peat deposits, sometimes to the treeless moor, more 

 frequently to the Waldmoor. 



But many matters still await explanation, among them some 

 which the writer hoped to explain as result of this study. And 

 they are likely to wait long. No extensive coal field has been 

 studied closely; in spite of the imposing array of skeleton sections, 

 there is an astounding lack of detail respecting many matters which 

 appear to have no important bearing on commerce. Until the topog- 

 raphy and geography of the Coal Measures land have been worked 

 out, geologists must be content merely with probabilities concerning 

 the remarkable bifurcation of some coal beds, the variations in sub- 

 ordinate intervals between two approximately parallel coal beds, the 

 presence of huge blocks of transported rock in coal and the asso- 

 ciated rocks, the immensely long periods of stable conditions indi- 

 cated by the thickness of some coals, and some others which will 

 suggest themselves to the reader. It is true that these are all purely 

 local in character, but they occur at many though somewhat widely 

 separated localities. The explanation for some of them must await 

 the solution of certain problems in physical and chemical geology, 

 lying wholly outside of the questions considered in this memoir. 



These matters, however, do not concern the general problem with 

 which this study has been concerned. In the present state of knowl- 

 edge, as revealed in the literature, that finds its solution in autochth- 

 ony alone. 



