280 R. Chalmers — Pre- Glacial Decay of Rocks. 



are coarser and often contain pebbles and bowlders of consider- 

 able size, the finer matter having evidently been carried away by 

 post-glacial denudation. In the hilly districts bordering the 

 Bay of Fundy, talus was observed at the base of the slopes in 

 a few places. On the Cambrian and Cambro-Silurian this 

 debris is finer and where slates prevail the materials are in 

 loose, fissile beds, i. e. they occur in the form of thin laminae 

 or scaly fragments of all sizes lying in the same position as the 

 original strata. Materials of this kind were observed in the 

 southern counties of New Brunswick, also on the south side of the 

 St. Lawrence near Quebec. The decayed rock upon these and 

 the older formations is less gravelly and sandy than upon the 

 Carboniferous sandstone areas, as might naturally be supposed. 



In many parts of the Maritime provinces these decomposi- 

 tion products were observed to have been only partially or 

 slightly acted upon by the Pleistocene ice. In this condition 

 they seemed to contain the same angular pebbles or gravel as 

 the rotten rock in situ beneath, but were shifted greater or less 

 distances from their original position by glacier-ice, and the 

 interstices filled with a bluish or gray clay, or sandy clay, as 

 the case might be, which baked hard on exposure. Beds 

 of this kind usually graduate upwards into true bowlder-clay. 



The occurrence of such extensive sheets of decomposed 

 sedentary rock in the region under consideration, much 

 denuded as they seem to be, points to the former existence of a 

 universal mantle of this material overspreading the country 

 everywhere in Tertiary and preceding ages, probably from the 

 first appearance of dry land. It was, however, partly modified 

 by the same agencies as are in operation around us at the pres- 

 ent day, namely by rivers, lakes, rain, snow, etc., and in the 

 valleys, especially, was changed into deposits of stratified clay, 

 sand and gravel. During the glacial period this decayed rock 

 furnished the principal portion of the material constituting the 

 bowlder-clay, and also that of the overlying, modified, post- 

 glacial beds. 



Agencies which produced Decomposition of the Rocks. 



The indigenous materials under discussion appear to be the 

 result mainly of two different agencies — mechanical and chemi- 

 cal. Although it is not the purpose of the writer to enter into 

 details regarding these in the present paper, it may be stated, 

 that under the climatic conditions of this country, the most 

 important seem to be (1) the precipitation, and (2) the 

 carbonic acid of the atmosphere and of decaying vegetable 

 matter, the latter usually resulting in what is called oxidation. 

 The changes of temperature which have such a wide range in 

 these latitudes must also have exerted a direct influence in pro- 



