496 A. W. G. WILSON SHORELINE STUDIES ON ONTARIO AND ERIE 



stratified clays impervious to moisture, erosion is aided, and indeed 

 hastened, by the action of springs. Particularly during the winter 

 season, when the faces of the wave-cut cliffs are protected from the direct 

 action of the waves by shore ice, and when the flowage of ground water 

 through the sand beds is more or less retarded if not stopped, water tends 

 to accumulate in these beds along the base of the cliffs. In the early 

 spring, when the frost loosens, this accumulation of water carries out 

 considerable quantities of sand, particularly where it is fine textured, 

 undermining the overlying materials. The water also acts more or less 

 as a lubricant ; so that, once the imdermined materials start to slip, often 

 large blocks move down the faces of the cliffs lakeward and are brought 

 within the reach of the waves. The quantity of material thus brought 

 to the wave zone is very large. 



In the process of cliff formation by spring undermining, in a number 

 of places where interglacial sand, gravel, and clay beds with some inter- 

 bedded layers of till occiir, there are developed interesting amphitheater- 

 like openings in the cliffs, which from their form and origin may be 

 named "spring cirques." The undermining processes in these cases seem 

 to have been most active at first in a lineal direction, possibly developing 

 a subterranean channel along which the sand and water first flowed. In- 

 land some little distance from the shore cliff this channel has widened, 

 and in time, by the process of caving, a large amphitheater is opened 

 behind the cliff, with narrow ridges on the shore side between the amphi- 

 theater and the shore. This type of cliff erosion is well shown, on the 

 Lake Ontario shore near Newcastle and again at the Scarboro bluffs. 

 Similar forms are also found in the high cliffs on lake Erie west of Port 

 Eowan. 



The cliff erosion is greatly hastened by the burrowing of animals, par- 

 ticularly sand martins and kingfishers, and less frequently by ground- 

 hogs. The nests of the two birds mentioned are made at the back 

 of a burrow, 3 to 6 feet in depth, always dug nearly horizontally back- 

 ward into soft sand deposits. At times of excessive rains, or in the 

 springtime, when the frost is passing out of the ground, these old bur- 

 rows often act as channels through which water at first trickles, but 

 which it gradually widens and deepens until the outlet becomes a well 

 defined channel and the protecting sod cover above is undermined and 

 ruptured. 



During recent times the cliff erosion along the shores has been very 

 materially hastened by human agencies. In a small way the opening of 

 the nests of the birds before referred to, by predatory boys in search of 

 eggs, gives rains early access to the burrows. The writer knows of at 

 least one instance where an old kingfisher burrow has become a deep 



