On Cijcli's (if S,-<J'iiiiiiif<ititni. — W ill Hi iiix. '>^''> 
that thickness, we Avould expect that the epochs between succes- 
sive general (listurl)ances would be progressively longer as the 
<-ooling of the interior advanced. On this hypothesis, other 
things e([ual. the PaUeozoic ;eon l)etween the Lower Silurian and 
the Permian would be shorter than the Mesozoic. and this in turn 
shorter than the Cainozoic. But while these deductions seem 
well founded, we should be exceedingly cautioits about applying 
them too literally owing to the nnmifold and intricate aspects of 
this problem. There seems to be good ground, however, for 
accepting the general views here set forth. A general synchronism 
of crustal movements is but a corollary from the doctrine 
of the identity of geological formations on ditferent parts 
of the globe. The later fcjrmed mountains were undoubtedly 
•colossal compared with earlier ones. We have hut to compare 
the Green mountains (making due allowance for subsequent 
erosion) which were uplifted at the end of the Lower Silurian 
(Dana) with the Rockies, Andes, and Himalayas of Tertiary times 
to realize the greater etl'ectiveness of orogenic forces with the aug- 
mented thickness of crust. While we seem forced to admit a 
general synchronism in tiie movements of continents as shown in 
the Eocene period, yet a close parallelism in the cycles of sedi- 
mentation should not V)e expected. Circumstances too numerous 
;ind complex to l»e here consideri'd would modify in endless ways 
the minuter adjustments and readjustments of land and sea. But 
this al)sence of parallelism does not :\t :dl inv;did:ite the genend 
doctrine of cycles of sedinu-ntation. 
Here it would be interesting to point out tiie relations 
sul>sistiiig between cycles of sedimentation ;iinl geological 
f:mnas. .1 jiritiri we feel sure thiit intimatt' connections 
nuist exist between the two. :ind the genei-:il facts of pahe- 
ontology seem to sustiiin the iuferi'nce. The modifying in- 
tluences of such cycles must luive profoundly :itfcctcd the 
development of ;\niin:il types. Hut we :ire too ignor:int of 
the laws of life to si)eculate upon the hkkIus (i/iiniiKh' of sucli 
developments. We can conjecture this much, howevei-. when 
the elevation of the hind is greatest, the denudiition is most ener- 
getic, the roily waters will tlien Mow farthest out into tin- sea. 
:ind only mud-loving tinimals will fre(|uent the neighl)orhood of 
the shores. Their renniins will !>(> imbedded in tiie resulting con- 
ulonu'riite. With the diminution of erosive activities new con- 
