Miscellaneous. 



to supply them with food; for the spongy texture of such plants 

 make them prone to decomposition. The paucity of animal re- 

 mains at this period, and their very unequal distribution, indicate 

 that the conditions necessary for the support of animal life were not 

 yet generally established. As we reach the silurian rocks, we dis- 

 cover that the conditions for organic life have become more favour- 

 able, and consequently we find a much greater variety of forms ; 

 but we are still struck by the paucity of vegetable remains. Doubt- 

 less these were present in quantity sufficient to supply food to the 

 marine animals which existed, but their perishable tissues have 

 yielded to the elements of destruction, and disappeared. The upheaved 

 land during the grauwacke and silurian systems seems to have been 

 too limited to favour the production of terrestrial plants. 



The disturbances which ensued after the close of the primary 

 period, rendered the earth more adapted for vegetation. Land was 

 upheaved, and the energetic causes then in operation must have 

 materially assisted in effecting its disintegration. The time which 

 elapsed between the close of the primary, and commencement of the 

 secondary periods, would be employed in the formation of soils on 

 this upheaved land. Soils formed from the detritus of the primary 

 rocks would be eminently adapted for a luxuriant vegetation, such 

 as existed during the deposition of the carboniferous strata. 



But no means of removing the excess of carbonic acid of the air 

 having been yet in operation, terrestrial plants could not be accom- 

 panied by terrestrial animals. It is obvious that this excess of 

 carbonic acid could not be very detrimental to the life of marine 

 animals ; because the sea, saturated as it is with salts, can only hold 

 a certain quantity in solution. But still the sea also must have 

 contained considerably more of this gas then, than at the present 

 day. The scantiness of vegetation was the great characteristic of the 

 primary strata ; but in the coal systems, this vegetation is marvellous 

 in its extent. The principal deposits in the series are arenaceous, ar- 

 gillaceous, and calcareous. The calcareous deposits of the primary 

 period, even as high as the upper silurians, occur in detached masses, 

 forming no continuous beds, like the carboniferous, or mountain lime- 

 stone. We find a total absence of land reliquiae in these calcareous 

 beds. Add to this, that, besides the nature of their fossil remains, they 

 afford evidences of a very tranquil and gradual deposition; and it is 

 apparent they must be of a marine origin. The excess of carbonic 

 acid dissolved by the water from the atmosphere, would render the sea 

 capable of retaining a large quantity of carbonate of lime in solution. 



