GENERAL RESULTS. 401 
complex organ the eye, selected from each ex- 
treme, and from a midway place in the progressive 
series of animal creations. We find in Trilo- 
bites of the Transition rocks, which were among 
the most ancient forms of animal life, the same 
modifications of this organ which are at the 
present time adapted to similar functions in the 
living Serolis. The same kind of instrument 
was also employed in those middle periods of 
geological chronology when the Secondary strata 
were deposited at the bottom of a warm sea, in- 
habited by Limuh, in the regions of Europe 
which now form the elevated plains of central 
Germany. 
The results arising from these facts are not 
confined to animal Physiology ; they give infor- 
mation also regarding the condition of the an- 
cient Sea and ancient Atmosphere, and the 
relations of both these media to Light, at that 
remote period when the earliest marine animals 
were furnished with instruments of vision, in 
which the minute optical adaptations were the 
same that impart the perception of light to Crus- 
taceans now living at the bottom of the sea. 
With respect to the waters wherein the Trilo- 
bites maintained their existence throughout the 
entire period of the Transition formation, we 
conclude that they could not have been that 
imaginary turbid and compound Chaotic fluid, 
from the precipitates of which some Geologists 
GEOL. I> D 
