Miscellaneous. 



437 



have been produced this way. But it is possible the thin layers 

 of limestone which occasionally alternate with the shale, sandstone, or 

 coal, in the coal formation, may be due to such a cause. Or might 

 we not conceive that the bituminous limestone shale might also owe 

 its production to this? The immense mass of undivided mountain 

 limestone could by no possibility have been thus produced, but may 

 have well been, by the deposition from solution through the instru- 

 mentality of the causes I have formerly described. Once allow, with 

 many geologists, that the ocean was in a heated state during a great 

 part of the primary period, and we are furnished with another 

 mighty means of abstracting the carbonic acid from the atmosphere. 

 The heated waters of the ocean could not dissolve carbonic acid, 

 but as they cooled this gas would be absorbed from the superin- 

 cumbent air ; and the water which evaporated and again descended 

 as rain, would bring down in solution large quantities both of car- 

 bonic acid and ammonia. 



Taking such things as these into consideration, together with 

 their possibility or probability, it is obvious that we have lost all 

 data for calculating the amount of carbonic acid in the air, at the 

 commencement of the secondary period. Allowing them even a 

 shade of probability, we could not deny that the former atmosphere 

 may have contained more than twenty times the amount of carbonic 

 acid that it does at present ; and admitting that it did so, we can 

 account for the extraordinary luxuriance of the primeval vegetation, 

 and for the absence of land animals whilst that vegetation lasted. 



During the period at which the carboniferous strata were de- 

 posited, neither reptiles, birds, nor mammalia appear to have existed : 

 nor was it possible that they could have existed, were these views of 

 the state of the atmosphere correct. 



It is not my intention to detain you, nor is it my province to 

 wander with you step by step over the various geological epochs. 

 In our brief sojourn in the carboniferous strata, we have seen that 

 several, possibly many causes, were in operation to remove carbonic 

 acid from the air, and consequently to fit it for the support of animal 

 life. But let us not suppose that these causes ceased with the ter- 

 mination of the carboniferous era. They still operated though in a 

 less striking degree during all the divisions of the secondary period ; 

 but during the deposition of the new red sandstone, they appear to 

 have been in a great measure dormant. It is the duty of the 

 geologist to explain what physical causes then existed which were so 

 unfavourable to animal and vegetable life. But the causes which acted 



