98 Froceedings of the Eoyal Physiccd Society. 



entombment on the spot of lagoon vegetation flourishing in 

 the shallower swamps of deltas that are subsiding inter- 

 mittently and with minor oscillations of level, has very 

 generally been recognised as the most probable mode of 

 formation of coal seams. Lastly, coal may be formed through 

 the sub-thalassic accumulation of deciduous vegetable matter 

 floated seawards from riparian forests. The author regarded 

 each and all of these various modes as having shared in the 

 formation of the various coal seams known to geologists, and 

 especially dwelt upon this as one of the many proofs that 

 identical results, in the operations of natural causes, may be 

 brought about in a considerable variety of ways. 



Leaving any further notice of those modes of formation of 

 coal seams that have been already fully recognised, the 

 author proceeded to discuss in some detail the mode referred 

 to last of all. It was pointed out that where large rivers, 

 draining tropical areas, are transporting, as they usually do, 

 a mixed burden composed of both organic and inorganic 

 substances, these latter, having a higher specific gravity than 

 the greater part of the vegetable matter, are the first to be 

 sedimented. This usually happens within a variable, bub 

 generally a short, distance from the land. Animal organisms, 

 as a rule, are also deposited at no great distance from the 

 land ; as are also such vegetable organisms as have under- 

 gone lengthy maceration, and have become water-logged at 

 this point. Such floating trees, for example, as have 

 travelled long distances, often sink amongst the coarser 

 mineral sediment, root downward, and become entombed in 

 that position as " snags." The smaller boughs, stems, fronds, 

 and leaves may float to greater distances ; but may subside 

 through the water at a rate sufficiently high to admit of 

 their reachino: the sea- bottom where the sedimentation of 

 the finer mineral matter is in progress. But the lighter 

 deciduous parts of the vegetation, and especially the spores 

 and such organisms whose chemical composition and whose 

 form both enable them to float long, remain in suspension 

 long enough to admit of their transportal to great distances, 

 and they are thus gradually carried by the marine currents 

 to zones far outside those attained by any other material 



