25O THE GROWTH OF COAL 



ferous, that we find an abundance of forms not essentially 

 different from those of the Carboniferous, though similar in 

 details. Only a few and very small beds of coal were accumu- 

 lated in this age ; but there was an immense abundance of 

 bituminous shale enriched with the macrospores of Rhizocarps. 

 The Ohio black shale, which is said to extend its outcrop 

 across that state with a breadth of ten to twenty miles, and a 

 thickness of 550 feet, is filled with macrospores of Protosalvinia, 

 as is its continuation in Canada. 



Above the great coal formation the Permian and Jurassic 

 contain beds of coal, though of limited extent, and formed in 

 the case of the two latter of very different plants from those of 

 the Carboniferous. In the Cretaceous and Tertiary ages, 

 after the abundant introduction of species of forest trees still 

 living, coal making seems to have obtained a new impulse, so 

 that in China and the western part of America there are coals 

 of great extent and value, all made of plants ot genera still 

 existing. In the Cretaceous coal of Vancouver Island there 

 are remains of such modern trees as the Poplars, Magnolias, 

 Palmettos, Sequoias, and a great variety of other genera still 

 living in America. Out of the remains of these, under favour- 

 ing conditions, quite as good coal as that of the coal formation 

 has been made, although the plants are so different. There 

 is, indeed, reason to believe that those now rare trees, the 

 Sequoias, represented at the present time only by the big trees 

 of California, and their companion, the redwood, were then 

 spread universally over the northern hemisphere, and formed 

 dense forests on swampy flats which led to the accumulation of 

 coal beds in which the trunks and leaves of the Sequoias 

 formed main ingredients, so that Sequoia and its allies in this 

 later age take the place of the Sigillariae of the coal formation. 

 Last of all, coal accumulation is still going on in the Ever- 

 glades of Florida, the dismal swamp of Virginia, and the peat- 

 bogs of the more northern regions. So the vegetable kingdom 



