PART 11. CHAPTER XXI. 



257 



Erect Position of Trees in the Coal Strata. 



surrounding sea — a zone several thousand miles in circumference. 

 No less than 57 species of ferns, some few of them arborescent, 

 have been already discovered in this country ; and what is re- 

 markable, one tree-fern ranges in this country as far south as the 

 46th degree, south latitude. There are no indigenous mammalia 

 except one rat, and a species of bat ; few reptiles, and none of 

 large size ; so that we may anticipate a total absence of the 

 bones of land quadrupeds, and a scarcity of those of reptiles, in 

 the modern estuary and lacustrine deposits of this region. That 

 there are lacustrine strata now in progress is certain, since one 

 lake called Rotorua, in the interior of the northern island, is said 

 to be 40 miles long, and receives the waters of many small rivers 

 and torrents.* 



The minor repetitions of alternate fresh and saltwater strata 

 in the Coal, have been ascribed to such changes as may annu- 

 ally occur near the mouths of rivers ; but when shale and grit, 

 containing coal and freshwater shells, are covered by large masses 

 of coralline rock, and these again by other Coal-measures, we 

 must suppose great movements of elevation and subsidence, like 

 those by which I endeavoured to explain, in Chapters XVI. and 

 XVIII., the superposition of the Cretaceous group to the Wealden, 

 or the alternations of argillaceous and calcareous rocks in the 

 Oolite. In adopting such views, we must suppose the lapse of 

 vast periods of time ; as the thickness of the Coal strata, in some 

 parts of England, independently of the Mountain limestone, has 

 been estimated at 3000 feet. Besides, we can by no means pre- 

 sume that all coal-fields were in progress at once, much less that, 

 in the same field, each mass of strata which is parallel, or occu- 

 pies a corresponding level, was formed simultaneously. It is 

 far more consistent with analogy to suppose that rivers filled up 

 first one part of a fiord, gulf, or bay, nearest the land, and then 

 another; so that the sea was gradually excliided from certain 

 spaces which it previously occupied. This is doubtless the cause 

 why the coal-bearing strata are generally uppermost, and the 

 Mountain limestone the lowest part of each series ; and why, in 

 certain districts in the S. W. of England, the Mountain limestone 

 suddenly thins out, so that coal-shales and grit rest immediately 

 upon older and unconformable rocks. 



Erect position of fossil trees in the Coal strata. — A great 

 number of the fossil trees of the Coal are in a position either ob- 

 lique or perpendicular to the planes of stratification. This singu- 

 lar fact is observed on the Continent as well as in England, and 

 merits great attention, not only as opening a curious field for 



* Account of New Zealand, published for New Zealand Association. 



