58 TRANSITION SERIES. 



The strata in which these vegetable remains have been 

 collected together in such vast abundance have been justtv 

 designated by the name of the carboniferous order, or great 

 coal formation. (See Conybeare and Phillips's Geology of 

 England and Wales, book iii.) It is in this formation 

 chiefly, that the remains of plants of a former world have 

 been preserved and converted into beds of mineral coal; 

 having been transported to the bottom of former seas and 

 estuaries, or lakes, an^d buried in beds of sand and mud, 

 which have since been changed into sandstone and shale. 

 (See PI. 1, sec. 14.*) 



* The most cliaracteristic type that exists in this countr}' of the general 

 condition and circumstances of the strata composing the great carbonife- 

 rous order, is found in the north of England. It appears from Mr.Fors- 

 ter's section of the strata from Newcastle-upon-Tyne to Cross Fell, in 

 Cumberland, that their united thickness along this line exceeds 4,000 

 feet. This enormous mass is composed of alternating beds of shale or 

 indurated clay, sandstone, limestone, and coal : the coal is most abundant 

 in the upper part of the series, near Newcastle and Durham, and the 

 limestone predominates towards the lower part; the individual strata 

 enumerated by Forster, are thirty two beds of coal, sixty-two of sand- 

 stone,, seventeen of limestone, one intruding bed of trap, and one hundred 

 and twenty-eight beds of shale and clay. The animal remains hitherto 

 noticed in the limestone beds are almost exclusively marine ; hence we 

 infer that these strata were deposited at the bottom of the sea. The 

 fresh-water shells that occur occasionally in the upper regions of this 

 great series show that these more recent portions of the coal formation 

 were deposited in water that was either brackish or entirely fresh. It 

 has lately been shown that fresh water deposites occur also occasionally in 

 the lower regions of the carboniferous series. (See Dr. Hibbert's ac- 

 count of the limestone of Burdie House, near Edinburg; Transactions of 

 the Royal Society of Edinburg, vol. xiii. ; and Professor Phillips's Notice 

 of fresh-water shells of the genus Unio, in tlie lower part of the coal 

 series of Yorksiiire; London Phil. Mag. Nov. 1(S32, 349.) The causes 

 which collected these vegetables in beds thus piled above each other, and 

 separated by strata of vast thickness, composed of drifted sand and cla}', 

 receive illustration from the manner in which drifted timber from the 

 existing forests of America is now accumulated in the estuaries of the 

 great rivers of that continent, particularly in the estuary of the Mississippi, 

 and on the River Mackenzie. See Lyell's Principles of Geology, 3d edit 



