56 THE TESTIMONY OF THE ROCKS. 
fourths of all geological time. From their great persist- 
ence in time (accepting, for the sake of argument, the 
“ages” of speculative geology) it would seem that they 
had a remarkably good opportunity to make wonderful 
progress in structure. During that time there were 
thousands of species, yet they made no progress. We do 
not know that in all those “millions of years” a single 
higher form was evolved from any one of the great mul- 
titude of species of trilobites. As Darwin says of the 
goose, so one may say of the trilobite; it “had a singu- 
larly inflexible organization.” The remarkable thing 
about this, however, is that previous to the “Primordial,” 
while it was becoming a trilobite, it must have had a 
singularly flexible organization, otherwise it could not 
have obtained its complex structure; but when it reached 
the “Primordial” it became very conservative. 
Fairhurst says, in the work already quoted: 
“It is a most remarkable fact that in the first geologi- 
cal period in which undoubted fossils occur, all the sub- 
kingdoms except that of the vertebrates are well repre- 
sented, and that there is no evidence from fossils that 
one sub-kingdom, or even that different classes of the 
same sub-kingdom were evolved from each other. The 
great gulfs that separate the animal kingdom into sub- 
kingdoms and classes existed then, and have continued 
till the present time. . . . If we rely on known fossils as 
evidence, we would be obliged to conclude that highly 
organized fishes were suddenly introduced. The break 
in the supposed chain of evolution between the inverte- 
brates and the highly organized vertebrates of the Lower 
Silurian is one of the greatest in the whole geological 
record. The vast gulf between these structures must, I 
think, remain unbridged except by the imagination.” 
