THE MODE OF ORIGIN OF COAL 219 



apparently present themselves, when the strata below (under- 

 clays, etc.) or above (roof strata) the actual coal beds are considered. 

 We have as a consequence the two opposed schools of opinion in 

 regard to the origin of coal. The hypothesis which homologizes 

 the coal bed with an existing peat deposit is known as the autoc- 

 thonous or in situ theory. On the other hand, the view that coal 

 represents an accumulation by floating and sedimentation in the 

 bottom of open lakes or lagoons is known as the transport or 

 allocthonous hypothesis. The evidence for and against these two 

 opposed views has recently been so admirably summarized by 

 Professor John J. Stevenson in his Formation of Coal Beds that it 

 appears unnecessary to refer to the subject further at this time. 



The purpose of the present communication is to emphasize the 

 importance of the study of the coal itself, in connection with any 

 views as to its composition and mode of origin. The investigation 

 of coal by means of the microscope has presented many dififiiculties, 

 chiefly because of the opacity and texture of the coal itself. The 

 methods which have been successful in the case of other minerals 

 have not given satisfactory results in the case of coal. The thin 

 ground sections of the mineralogist and petrologist are of little 

 value when the material investigated is coal. If the ground sections 

 are made thin enough to show all of the structural features, these 

 are destroyed by the abrasive effect of the process on the com- 

 paratively soft and friable substance of the coal itself. The writer 

 has had considerable experience in investigating the remains of 

 fossil plants in a carbonized condition, a state of preservation which 

 has hitherto been neglected in favor of petrified material. Material 

 in a mineralized condition of preservation is, however, compara- 

 tively rarely available, while carbonized vegetable remains are 

 often abundant. A modification of the writer's methods in the case 

 of carbonized Mesozoic plants has been developed as the result of 

 a long series of experiments, and it is now possible to secure 

 satisfactory thin and transparent sections on the microtome of prac- 

 tically all kinds of coals. Obviously this possibility put the ques- 

 tion of coal composition and mode of formation on an entirely new 

 footing, as it is now possible to investigate these subjects satis- 

 factorily from the standpoint of the organization of coals of various 



