OTTAWA VALLEY CONCRETIONS 629 



their long axis only two or three times greater than the transverse axis 

 and generally approximately parallel to or forming a slight angle with 

 the bedding planes instead of traversing them at right angles, as the 

 ordinary root concretions do. These structures, which are seldom more 

 than 3 or 4 inches in length, clearly represent an early stage of concre- 

 tionary growth, which, like that of the cylindrical form just described, 

 is doubtless in progress at the present time. The specimens figured were 

 collected by W. A. Johnston, who first brought this structure to the 

 writer^s notice. Continued development might be expected to produce 

 from them forms resembling certain subcylindrical cryptozoons. The 

 stratigraphic relations of the concretions of the upper clays are shown in 

 figure 2. 



PLEISTOCENE SAND AND SHELL CONCRETIONS 



A fourth type of concretion which occurs only at certain localities in 

 the upper or superficial layers of the Pleistocene sands has the shape 

 roughly of a small slender icicle and stands vertically in the beds holding 

 it. A small root or the cavity left by its decay invariably traverses the 

 center of these root-like concretions. The concretions have no resem- 

 blance in form to those found in "the lower beds. Their general shape 

 and contour is controlled very definitely by the root nucleus. In compo- 

 sition they are largely carbonate of lime, which has cemented together 

 the sand adjacent to the root nucleus. The degree of induration ex- 

 hibited by them varies greatly, some specimens crumbling almost as 

 easily as the adjacent sand. Others have a firmness approaching that of 

 limestone, while some specimens show a very perfect cementation of the 

 sand and the hardness of fiint. 



The distribution of the icicle or root shaped concretions in the super- 

 ficial beds of the Pleistocene sands is likewise confined to a few localities 

 where conditions were especially favorable to their formation. One of 

 these localities is the upper slope of the sand terrace at the sand pits 

 near Rideau Junction (figure 3). They also occur in extraordinary 

 abundance in the fine-grained sandy beds on the shore of Lake Ontario 

 opposite the Presqu'ile summer hotel (plate 11, figures 1-4). They may 

 be seen at various other localities in the Pleistocene sands of Ontario. 



It appears obvious that the small rootlets found in the center of the 

 icicle-shaped concretions of the Pleistocene sands have been the initial 

 factor in their formation. It will hardly be questioned that the small 

 roots frequently found in the center of these concretions through the 

 development of humous acids have led to the segregation of the calcareous 

 ■constituents of the sands in which they were growing, thus leading to 



