256 Dr. Whcelton Hind — Zones of the Carboniferous. 



which the deposit accumulated was practically level over the same 

 extent. 



As a rule, fossils are not equally distributed through Carboniferous 

 strata. Many feet of limestone beds contain nothing beyond 

 microscopic forms of life, but every here and there the beds are 

 crammed with fossil remains, generally speaking, not in the 

 condition in which they lived, but Bivalves and Brachiopods often 

 have their -valves separated and are filled with other shells, and 

 many forms which probably did not exist at the same depth are 

 found together though the shells are not rolled. 



The value of life zones can be well understood in a series of 

 strata which was deposited without intermission on a floor which 

 was sinking at a uniform rate, without oscillations of level ; but 

 even in such a case the beds deposited on the same line of 

 accumulation, near the shore and out at sea, would contain a very 

 different fauna. I shall show later on that such a condition 

 of deposit was anything but characteristic of Carboniferous times. 



While, therefore, life zones are not altogether to be relied upon 

 in the identification of strata in widely separated areas, neither 

 can they be regarded with any degree of absolute accuracy as indices 

 of the contemporaneity of an extensive horizontal deposit, though 

 similar faunas indicate similar conditions of deposit. Every ocean 

 connotes a shore, and it is therefore obvious that deep-sea life 

 is contemporaneous with littoral and terrestrial forms, and that in 

 a slowly-sinking area, littoral, terrestrial (fluviatile), and pelagic 

 forms would be entombed along the same line of sedimentary 

 deposit, at any rate at right angles to the retreating shore-line, 

 though narrow belts parallel to that line might be characterized 

 by the presence of the same fauna at definite horizons. 



If deposition were going on in a rising area the shore-line would 

 gradually advance, and littoral deposits would be formed above the 

 pelagic ; but if, on the other hand, the area were gradually sinking, 

 the marine sediments would be superimposed upon the littoral, and 

 thus contemporaneous faunas would become successive. 



The greater part of the Carboniferous areas of Great Britain 

 consists of recurring series of sandstones, clays, coals, and lime- 

 stones, indicating clearly a repeated oscillation of level, with 

 intervening periods of rest, during which the terrestrial conditions 

 necessary for the growth of the coal flora obtained. Such a series 

 of oscillations could only result in repetitions of the faunas typical 

 of terrestrial, littoral, and marine conditions at different horizons in 

 the same vertical series. A good example of this state of things is 

 to be found in the beds of the Calciferous Sandstone series of the 

 Fifeshire coast. This series has been splendidly worked out by 

 Mr. James Kirkby (Quart. Journ. Geol. Soc, vol. xxxvi, 1880, p. 559). 

 Here, in 3,800 feet of strata, several marine bands occur separated 

 by various depths of intervening beds, and containing a large and 

 varied fauna of typical marine facies. True, that the fauna in each 

 of these marine beds is not absolutely identical ; but many of the 

 same species recur in several of them. The intervening beds are 



