PALEONTOLOGICAL GEOLOGY 
327 
able circumstances it is not probable that the lowering of temper¬ 
ature ever amounted to very much, and certainly not enough to 
be critical for the Tetracoralla. 
Ge:orge M. Hall. 
Lowering of Life's Record into the Abyss of Time. Speaking 
from the viewpoint of a morphologist the late Professor W. K. 
Brooks once made a striking statement that one standing on the 
brink of Cambric seas could get no better prospect of life that had 
gone before than one does today. Despite the necessary inference 
that the paleontologist need not hope to ever unearth fossils es¬ 
sentially different from those which he now knows from the Cam¬ 
bric rocks and that these really approximate the forms which 
existed when life first became established on the bottom of the 
sea pre-Cambrian fossils will yet be long sought. 
Since Brooks’ observation of 30 years ago pre-Cambrian re¬ 
mains of organisms have come to light in abundance. Both in 
the Belt Mountains of Montana, and in the Lake Superior region 
pre-Cambrian forms are now known. In past attempt to discover 
fossils in strata older than those of Paleozoic age a most serious 
obstacle to success always is the highly altered condition of the 
ancient rocks whenever they are exposed to view. The well- 
known geologic law that the older a rock is the more metamor¬ 
phosed is it likely to be especially applies to the pre-Cambrian 
formations. It is a criterion of such great weight that it is still 
a decisive factor in the determination of the relative ages of these 
old rocks. In the majority of cases known metamorphic processes 
have gone on so long and so intensely that it is often almost impos¬ 
sible to tell whether a rock-mass was originally igneous or sedi¬ 
mentary in character. 
Great significance must be attached to the establishment of the 
antiquity of the oldest fossil fauna as indicated by the finding of 
the organic remains in the pre-Cambrian Marquettan strata of 
the Steep-Rock Lake district. At a single step these fossils carry 
back the record of life on our planet beyond the middle of Arche¬ 
ozoic time, or a chronologic distance nearly twice as long as all 
Paleazoic time. Even the fossil horizons of the Beltian section, 
according to the best calculations, are well towards the base of the 
Proterozoic succession, the next eral span behind the Paleozoic 
