1864.] NATURAL HISTORY SOCIETY. 221 



grand order of succession in the [Laurentian system seems to be 

 the same with that so often repeated in other parts of the geo- 

 logical scale, — coarse fragmentary beds represented by conglomer- 

 ate and gneiss ; calcareous and fossiliferous bands represented by 

 the Eozoou limestones ; and finer earthy deposits, represented by 

 felspathic rocks. This brings the Laurentian into a cycle some- 

 what similar to that of the Potsdam sandstone, the Chazy and 

 Trenton limestone, and the Utica slate and Hudson Eiver in the 

 Lower Silurian ; or to that of the Medina sandstone,the Niagara 

 limestone, and Lower Helderberg in the Upper Silurian ; or to that 

 of the Oriskany sandstone, Corniferous limestone, and Hamilton 

 and Chemung groups in the Devonian ; or to that of the Lower Car- 

 boniferous conglomerates and sandstones, the Carboniferous lime- 

 stones, and the Coal-measures in the Carboniferous period. This 

 recurrence of cycles of deposit cannot be accidental. It is more or 

 less to be seen throughout the geological scale, and in all countries ; 

 and as I have elsewhere pointed out, it includes numerous subor- 

 dinate cycles within the same formation, as in the coal-measures. 

 Eaton, Hunt, and Dana have referred to it; but it deserves a more 

 careful study as a means of settling the sequence of oscilla- 

 tions of land and water in connection with the succession of life. It 

 will also be important in giving fixity to our geological classifications, 

 and may eventually aid in establishing more precise views of the 

 dynamics of geology and of the lapse of geological time. The prog- 

 ress of the earth has, like most other kinds of progress, been not 

 by a continuous evolution, but by a series of cycles, of great summers 

 and winters, or days and nights, of physical and vital changes, in 

 each of which all things seem to revolve back to the place of begin- 

 ning ; only to begin a new cycle or new turn of a spiral, similar to 

 the last in its general course, though altogether difi'erent in its 

 details, accompaniments, and results. 



There is another subject of great geological importance on which 

 the publication of the Report enables strong ground to be taken. 

 I refer to the conditions under which the Boulder-Drift of Canada 

 was deposited. It has been customary to refer this to the action of 

 ice-laden seas and currents, on a continent first subsiding and then 

 re-elevated. But this opinion has recently been giving way before 

 a re-assertion of the doctrine that land-glaciers have been the 

 principal agents in the distribution of the boulder-drift, and in the 

 erosions with which it was accompanied. I confess that I have stead- 



