258 DISSERTATION ON THE ATMOSPHERE. 
the characteristic of nitrogenised food to figure in the com- 
pound ammonia. 
Now we have traced a constant source of carbonic acid, of 
water, and of ammonia. We have seen that what might 
appear at first view distinct and separate is in reality one. 
That man, the chief glory of creation, physically is but 
matter full grown and finely elaborated ; so exquisitely per- 
fect indeed that a degrading action becomes essential to 
farther advance. 
Hence a process of reduction begins and continues until 
such time as a basis alone remains coherent for a new struc- 
ture — a new instrument of thought. Verily, death and life 
are an atomic Alpha and Omega. Although we may still 
endorse what w r as said by Descartes two centuries ago — 
“ In pliilosplii nihil adhuc reperi de quo non in utramque partem dis- 
putatur.” 
We shall probably now be better able to retrace our steps. 
Three historical periods demand separate discussion. Geo- 
logically speaking, they constitute the primary* secondary, 
and tertiary formations ; but, more to the point, the periods 
respectively of plants, of fish, and of mammals, the last 
immediately preceding the era of man. Such is the order 
of creation, according to inspired record, such indubitably 
the order from all physical knowledge. Mark the link-like 
progress in an onward direction. Observe how, from 
tumultuous chaos, order issues, and from simplest order the 
finest harmony. 
First in course of time occurs what was emphatically 
the era of plants bearing seed after their kind. The problem 
which rises before us includes their food, its kind, origin, 
and degree. 
Now the fundamental strata of our globe — the primary 
formation — exhibits no form of extinct life whatever. Never- 
theless, the primary inorganic constituents yield proof that 
during their deposition, those compounds, at present deemed 
essential to the life of plants, existed. Thus carbonic acid 
must have been prevalent; the limestone proves it, and 
moreover renders it probable that the acid gas was derived 
from an incumbent atmosphere. Undoubtedly, during the 
primary period, and long prior to the formation of land, the 
ocean had a very high temperature, and partly to its conse- 
quent restless condition, is most likely due that irregular 
shape the primary strata possess. The water-worn charac- 
ter of these earliest lines betoken aqueous action, while of 
