J52 CARBONACEOUS DEPOSITS. 



Fig. 250. Sf.'rpula, on the inside of a 

 Fig. 241 ftmmoni'tes cate'na. Ca'rdium porulo'sum. 



This is pr jvod by the fact thai fre^u .ntly on the inside of shells we fmer 

 parasitic uninr.als, that attach the ns-il cr to bodies of all kinds (fig. 250), 

 and which could not attach themsel'-ef here, in the interior of the shell, if 

 the moJlusk had not been previously destroyed. Often the very shell of 

 the purisite is covered by others, showing that the first had long existed in 

 the ten. The shells of bivalves are frequently found separated, showing 

 the animal must have died before they were buried. And there are shells 

 wliich are pierced by lithopha'gi, as well as the flints and fragments of 

 limestone which accompany them, leading to the same conclusion. There 

 ure of course some exceptions, but these are commonly due to local circum. 

 stances. 



Generally, these shelly deposits are on the spot where the animals lived. 

 In fact, they contain a great number of uninjured shells, the most delicate 

 appendages of which are in a state of perfect preservation ; a circumstance 

 not reconcilable with the idea of transportation by currents, which would 

 have broken the whole and rounded the fragments. Even in decomposition, 

 the finest parts have left their impressions on the substances enveloping them. 



By means of the debris alluded to, we may always recognize marine 

 deposits. 



6. Carbona'ceoits deposits. It is undeniable, that the carbo- 

 na'ceous deposits found in different strata of the earth, were pro- 

 duced there by the accumulation of the remains of plants ; this IF 

 proved by the numerous and clearly characterized remains of 

 stems and leaves met with, either in the combustible mass or in 

 the earthy matter containing it. On this point al 1 are of one opinion ; 

 but all do not agree as to the manner of accumulation of these re- 

 mains. Some geologists suppose that all carbona'ceous deposits 

 result from the sinking of great rafts of divers plants, transported 

 by great rivers, by maritime currents, and sunk in different places; 

 others think, on the contrary, that most of these deposits were 

 formed, in place, in the same manner as peat-bogs, in depressions 

 of the surface to which rivulets daily brought debris from the sur- 

 rounding vegetation. 



6. From what are carbona'ceous deposits derived ? How are carbona' 

 ceous deposits formed ? 



