67 



Just as we have a great diversity of formations about Ottawa, 

 so also have we a great diversity of substances in the materials which 

 make up the rock of the Post-Tertiary deposits, (and let it be borne in 

 mind, that in using the word " rock" it is used in its true geological 

 sense, so that a handful of sand, a lump of clay, a mass of pebbles, 

 cemented or not by finer detritus, are all as much " rock" as a pillar of 

 freestone, a block of limestone or a column of granite). Most of the 

 materials which are found in these newer deposits were derived from 

 the older formations of the district, whilst erratic blocks, and the like, 

 may have come from great distances. To go into details regarding all 

 the kinds of rocks met with, would- necessitate a protracted study of a 

 great quantity of material which years of labour could not exhaust, and 

 which would form the consitituent elements of all the formations from 

 the Laurentian to the Hudson River as they ai-e developed in the 

 *' Ottawa Basin ;" from the gneissoid, granitic and hornblendic rocks 

 of the former, to the shaly magnesian and arenaceous measures of the 

 latter. There would be the gueisses, pegmeties, crystalline limestones, 

 serpentines, dolomites and diorites of the Loiver Laurentian, occurring 

 at Chelsea in the Laurentide Hills, there would also be included portions 

 of the conglomerates and quartzites and calc-bearing sandrock materials 

 peculiar to the unconformably overlying Potsdam and Calciferous for- 

 mations, whilst the sandstones, shales and limestones of the Chazy, 

 followed upwards without a break by the impui-e calcareous strata of 

 the Black River and Trenton formations would all be mixed together 

 with the likewise conformably overlying bituminous schists of the 

 Ut'ica. 



The materials which compose the series of formations just men- 

 tioned and newer than the Laurentian were themselves derived from 

 the Laurentian System, fur .this latter contains all the elements 

 necessary for the formatio^^ of the sandstones, shales and limestones of 

 the newer overlying <JamDro-Silurian or Ordoviciau strata. 



Having ascertained the series of strata whence the material was 

 obtained which constitutes the various beds in the Post Tertiary 

 deposits, let us consider the condition of affairs previous to and at the 

 coming in of the Glacial Epoch. 



