CONTRAPOSED SHORELINES! 
CHARLES EL CLAPP 
Geological Survey of Canada, Ottawa 
When a shoreline which has been cut in a soft mantle covering 
hard rocks is, through the complete retrogression of the mantle, 
placed against the hard rocks, it changes radically, since it becomes 
dependent on the character of the hard rock surface which was 
covered by the soft mantle. The development of this type of 
shoreline is analogous to the development of superposed valleys, 
and in referring to the type it is desirable to use some term that 
shall suggest this analogy. The simplest and most evident seems 
to be the term contraposed,’ meaning placed against (superposed 
meaning placed upon). 
By the development of a contraposed shoreline, a shoreline may 
change during a single cycle from mature to youthful. Early in the 
cycle when the shoreline is cut in the soft mantle it must be simple, 
nearly straight, and cliffed, submature to mature. As retrogression 
proceeds the soft mantle is pushed back to the hard rocks and 
gradually, since the hard rocks are more resistant, is retrograded 
beyond them. At such a point in the cycle the shoreline is entirely 
in the hard rock. Hence it is identical to one developed by the 
depression of a hard rock surface, and is consequently in a youthful 
stage. 
The accompanying block diagram illustrates three stages in the 
development of a contraposed shoreline. The far block indicates 
the conditions existing during the early part of the cycle, when the 
shoreline is cut in the soft mantle. The middle block indicates the 
conditions when the mantle is retrograded in places beyond the hard 
t Published with the permission of the Director of the Geological Survey of 
Canada. Acknowledgment is due Professors W. M. Davis and D. W. Johnson who 
suggested that I devise a name for the type of shoreline described. 
2 As superimposed has recently and conveniently been contracted to super- 
posed, contraposed is preferable to contraimposed. 
537 
