8 



NOTES ON CONCRETIONS 



which is a series of prismatic or vacerous lines 

 enlarged about ten diameters. 



See fig. 5,. 



FIG. 5. 



15. On the flat surface of the Potsdam sandstones, Upper 

 Cambrian, of the coast of Labrador, fine examples of concretion- 

 ary structure may be seen, some of them a yard or more in 

 diameter, showing fine concentric lines of various shades of 

 color which, when weathered, look like the lines of growth in a 

 section of a tree, but no radial lines are seen. The sandstone is 

 pierced by Scolithus Canadensis, (Billings). Fig. 6 is frornja. 

 sketch of a detached piece lying on the shore. 



FIG. 6. 



