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certain local and limited areas as capable of being aft^cted by the 

 agencies above mentioned, there is little doubt that they are together 

 wholly inadequate to explain the phenomena of striated surfaces (see 

 Prestwich's geology) over such vast areas, as it is known that these 

 surfaces extend, in some cases, for hundreds of miles. 



But, of the sedimentary strata which, during this pei-iod of 

 submergence, were being laid down over the remains of the glacial 

 epoch the lowermost series consists of bluish gray clays of more or lees 

 plasticity and vai-ying gi-eatly in thickness in different parts of this 

 region. There are a number of sections both liatural and artificial which 

 this district has afforded. Amongst the latter may be mentioned the 

 Rideau Canal, which from the " Basin " to the " Deep Cut " " gives a 

 very good idea of the thickness of these clays there. Then the hun- 

 dreds of sections which the recent excavations carried on by the City 

 Engineer have exhibited, where in almost every instance, the clays may 

 be seen in their normal position. Then come the brick-yards owned 

 by the Messrs. Odell, Cla^rk, Nicholson, Graham and others. In the 

 first mentioned of these have been found remains of a fossil sponge, the 

 Tethea Logani of Dawson, together v,'ith shells- and foraminifera and a 

 bone sent to Prof. Cope for identification, all of which were presented to 

 the writer through Mr. A. P. Low, of the Geological Survey of Canada. 

 But whilst artificial sections ai-e often more convenient in ascertaining 

 the relative thickness of the different kinds of strata, nevertheless, the 

 natural sections which are met with everywhere, enable us to obtain 

 the .geographical distributions, extent and thickness, sometimes with 

 greater facili'ty, as these sections are very numerous indeed. Along 

 the left bank of the Rideau River, e. g., from tlie Hog's Back to the 

 Falls, down the Ottawa as far as Green's Creek, and farther across the 

 river in Hull Township as far as Ironsides, and above that towards New 

 Chelsea, and in Nepean and Gloucester Townships, there are hosts of 

 natural sections, where the "Leda clay" formation so-called on account 

 of the pi'evalence of a small bivalve shell, LeJa ( Fortlandia) arctica, 

 Gray is well exposed. 



An interesting point about these clays and accompanying strata is 

 the fact tliat they occur in many instances in the shape of " terraces " 

 or small plateaus following one another at different levels. By one stand- 



