ONWARD THROUGH THE AGES. 133 



tion many years ago, but I believe no one has distinctly 

 enunciated it except that admirable geologist, Dr. Dawson, 

 of Montreal. Geological time has been marked off into 

 Ages, Periods, and Epochs by physical revolutions. These 

 were universal for the Ages, but more local for the subor- 

 dinate divisions of time. The commencement of every in- 

 terval of time was characterized, to some extent, by disrup- 

 tions, upheavals, violence, emission of heat and vapors from 

 beneath the crust, violent dashing of waters against coast- 

 barriers, destructive ocean tides and streams, and the more 

 or less complete extinction of living beings. Simultane- 

 ously, therefore, with the disappearance of a fauna from the 

 earth, the ocean's bottom was overstrewn with the coarse 

 debris of a geological revolution. As the shaken crust sub- 

 sided to a more quiet position, only the finer sediments 

 were transported to great distances from the shores. Last- 

 ly, when peace and stability were again restored, the vast 

 expanse of the ocean, as it floated over the area of North 

 America, was a calm and clear lagoon, in which lived and 

 labored those lime-loving animals which incase themselves 

 in shells, found coral structures, and eliminate from the 

 water the materials of limestone strata. There is, conse- 

 quently, for each period of the world's history a definite 

 succession of strata as to kind. These may be designated 

 Coarse-fragmental, Fine-fragmental, and Calcareous. The 

 Coarse-fragmental we style conglomerates, and their posi- 

 tion is at the bottom of a group of strata. The Fine-frag- 

 mental vary from sandstones to shales, and they rest upon 

 the conglomerates. The Calcareous constitute the lime- 

 stones which answer to the culmination of a geological in- 

 terval, and rest near the top of the group. The life of each 

 interval attained its full expansion during the Calcareous 

 epoch. Toward the close of this epoch the waters of the 

 sea began again to be turbid, from the premonitory jarrings 



