PRIESTLEY'S DISCOVERY OF OXYGEN GAS. 395 



and would premise that there is no fact better established in all the 

 range of physical science than that of Priestley's, heretofore men- 

 tioned, that plants grow at the expense of the atmosphere. I further 

 call to mind the indubitable fact that all coal, whether bituminous or 

 anthracite, is of vegetable origin ; that all the great deposits of these 

 carbonaceous materials, occurring in Europe, Asia, Africa, America, 

 and in the islands of the sea, for hundreds of miles in extent, and of 

 unknown thickness, are vegetable matters once formed under the in- 

 fluence of the sunlight, and existing as luxuriant forest-growths — 

 forests that in succession were entombed in the bowels of the earth. 

 There was then most assuredly a time when all this carbon existed as 

 carbonic-acid gas in the air, giving rise to an atmosphere in which, as 

 we know, animal life could not exist. But the sun had charge of the 

 matter, and as centuries rolled by he was extracting tliat poisonous 

 gas from the atmosphere, efiecting its decomposition, as he did for 

 Priestley, bringing forth from it vital air, oxygen gas, and getting 

 things ready for the appearance and continuance of animal life. 



I therefore regard, in a philosophical jjoint of view, the period of 

 the deposit of the coal as tlie great event in the earth's history. Those 

 who are familiar with the details of these things will recognize it as 

 the epoch which parts off a blank solitude on one side, broken by the 

 rude beginnings of low animal life, from that later period, on the 

 other, which is adorned by all the beautiful contrivances of animated 

 Nature, and crowned by the presence of man. The laws of Nature 

 have ever from the beginning been such as they are now. We are 

 fully able to trace the clear relationship between the condition of living 

 things on the surface of the earth and the constitution of the atmos- 

 phere ; and what chemistry says ought to have taken place in succes- 

 sive centuries, geology tells us actually occurred. Understanding the 

 changing condition of things as respects the air, we could predict the 

 corresponding changes in animated Kature, and the evidence that we 

 are right is engraved on the rocks and stamped on the ocean. 



So, therefore, we see that that relation which now exists betw^een ani- 

 mals and plants, and the atmosphere, is an affair that has sprung out 

 of a prior order of things — that there was a time when the constitu- 

 tion of the air was utterly unfit for the support of animal life; that a 

 purification took place through the action of the rays of the sun ; and 

 the deposit of coal marks out the great epoch when life of a high 

 order, among air-breathing animals, became a possibility. And is it 

 not interesting to remark how gradually, from a totally different order 

 of things, have sprung those great laws which determine not only the 

 fixity of the constitution of the air, but also the duration of species 

 and individuals ; that automatic, self-acting machine in which animal 

 and vegetable life are the opposing forces. 



In thu-s sketching out the course of events as we now know them 

 to have taken place in those ancient times, and in explaining how one 



