“xT PHENOMENA OF ORGANIC NATURE 377 
some particular bed or stratum which should con- 
_ tain the remains of those creatures with which 
_ organic life began upon the earth. And if we did 
so, and if gach forms of organic life were pre- 
_ servable, we should have what I would call his- 
L torical evidence of the mode in which organic life 
began upon this planet. Many persons will tell 
- you, and indeed you will find it stated in many 
_ works on geology, that this has been done, and 
_ that we really possess such a record; there are 
some who imagine that the earliest forms of life 
of which we have as yet discovered any record, are 
in truth the forms in which animal life began upon 
the globe. The grounds on which they base that 
" supposition are these :—That if you go through 
the enormous thickness of the earth’s crust and 
get down to the older rocks, the higher vertebrate 
animals—the quadrupeds, birds, and fishes—cease 
to be found; beneath them you find only the in- 
vertebrate mals: ; and in the deepest and lowest 
‘rocks those remains become scantier and scantier, 
“not in any very gradual progression, however, 
‘until, at length, in ead are supposed to be the 
_ oldest rocks, the animal remains which are found 
are almost always confined to four forms—Oldhamia, 
Be hose precise nature is not known, whether plant 
or animal; Zingula, a kind of mollusc; Trilobites, 
a Dcstanchh animal, having the same essential 
plan of construction, though differmg im many 
details from a lobster or crab; and Hymenocaris, 
SH PF pres i iia las 1 NE Oe meen: — — _ , 
