38 C. Lyell on the origin of Coal-fields. 
under marine or brackish water, the base of the trunks of the 
submerged trees being covered with serpule or a species of spi- 
rorbis. Not unfrequently seams of coal are succeeded by beds 
of impure bituminous limestone, composed chiefly of compressed 
Modiole with scales and teeth of fish, these being evidently de- 
posits of brackish or salt water origin. 
e lecturer exhibited a joint of the stem of a fresh water 
reed (Arundinaria macrosperma) covered with barnacles, which 
he gathered at the extremity of the delta of the Mississippi or the 
Balize. He saw a cane-brake (as it is called in the country) of 
these tall reeds killed by salt water, and extending over several 
acres, the sea having advanced over a space where the discharge 
of fresh water had slackened for a season in one of the river’s 
mouths. If such reeds when dead could still remain standing in 
the mud with barnacles attached to them, (these crustacea having 
been in their turn destroyed by a return of the river to the same 
spot,) still more easily may we conceive large and firmly rooted 
Sigillarie to have continued erect for many years in the Carbon- 
iferous Period, when the sea happened to gain on any tract of 
submerged lan 
Ss 
formation of Nova Scotia. The data he said for such an esti- 
mate are as yet imperfect, but some advantage would be gained 
could we but make some slight approximation to the truth. The 
Strata at the South Joggins are nearly three miles thick, and they 
are known to be also of enormous thickness in the district of the 
eastward. ‘There appears therefore little danger of erring on the 
side of excess, if we take half that amount or 7500 feet as the 
average thickness of the whole of the coal measures. The area 
of the coal-field, including part of New Brunswick to the west, 
and Prince Edward’s Island and the Magdalen Isles to the north, 
(or 51,136-4 cubic miles) of solid matter as the volume of the 
h an array of figures conveys no distinct idea to the 
mind; but is interesting when we reflect that the Mississippi 
would take more than two million of years (2,033,000 years) to 
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