OTTAWA VALLEY CONCRETIONS 621 



cretions of this part of the section^ if any exist. Above S-tO feet above 

 tide these deposits are of very limited extent and not known to contain 

 concretions. The beds to be considered in the following pages have there- 

 fore a thickness of only about 225 feet. A generahzed section of these 

 beds as seen between Ridean Junction and the month of Greens Creek is 

 shown below : 



RIDEAU RIVER AXD GREEXS CREEK SECTIOX 



Feet 

 Sand with some intercalated silty clay in lower part, containing Myti- 



his eduliis and Saxicava 65 



Clav, free from sand, finely laminated 20iir 



Silty blue-gray clay with red or brownish bands and numerous fossils. . 65 it 



Fine blue clay with Mallotus villosus, Portlandica arctica, etcetera.... ~d~ 



Total 225 



The difference between the three divisions recognized in the clays of 

 this section are not of the maomitnde or obvious character which usuallv 

 distinguish formations or even members of a formation. There are, how- 

 ever, differences which brick-makers recognize and which the contrasts 

 between the concretions found in them show to be real ones. 



Each of the four sets of beds recognized in the section is characterized 

 by concretions possessing certain group or family resemblances which 

 serve to separate them into easily recognizable groups corresponding to 

 the inclosing sediments in spite of their diverse features (figure 1 ) . 



Mrs. J. M. Arms Sheldon found in her studv of the Connecticut River 

 concretions that "each bed has a form of concretion peculiar to itself. 

 You wordd never, for instance, find a circular disk and a cylindrical clay- 

 stone imbedded together.*" *^ Essentially the same general statement can 

 be made concerning the Ottawa Pleistocene concretions and the sediments 

 holding them. It is proposed here to point out certain contrasts between 

 the concretions of the several beds of the marine clays, the non-marine 

 clays, and the sands at the top of the serie^. 



COXCRETIOXS OF THE LOWER CLAYS 



The concretions of the lower division of this series (number 1) fall 

 into two general classes with reference to the s}Tnmetry which they ex- 

 hibit. The most abundant concretions are those which approach more 

 or less closely the spheroidal tv'pe of S}Tflmetry. The most perfect of 

 these show a spheroidal form, wliich is nearly always greatly depressed, 

 the vertical beino- verv much shorter than the horizontal axis and at riofht 



" J. M. Arms : Can. Rec. Sci.. vol. 4, 1891. p. 23S. 



