BARRIER BEACHES 475 



Barrier teaches. — Small barrier beaches inclosing lagoons are found 

 at several localities along the north and south shores of the lake. In 

 practically ever}'^ instance they are to be attributed to the action of long- 

 shore transportation, whicli luis built them from materials derived from 

 the adjacent sea-cliffs. The more important of the bays or harbors in- 

 closed by these barriers are Burlington bay. Frenchman bay, Whitby 

 harbor, and Port Darlington harbor on the north shore ; Little Sodus bay, 

 Big Sodus bay, and Irondequoit bay on the south shore. 



The largest and most important of these barrier beaches is that at the 

 west end of the lake, known as Burlington beach. This consists of a low 

 beach ridge, built of sand and gravel, stretching across the west end of the 

 lake in such a way that it forms the third side of a triangular bay, nearly 

 equilateral in outline, at the west end of the lake. The bar has a surface 

 width of about 500 yards and a length of nearly 7 miles from shore to 

 shore. The greater portion of the material in the beach came from the 

 east along the south shore. At the north end, however, much of the 

 waste evidentl}^ came from the north shore of the lake. 



Special features: Presque Isle tombolo. — Lying about 2 miles off the 

 north shore of lake Ontario a few miles east of Lakeport is a low cuesta 

 of Trenton limestone, the crest of which lies nearly parallel to the 

 mainland. This rocky ridge, once prol)ably an island, is now tied to the 

 mainland by a long sand bar. At present the tie bar is about three- 

 quarters of a mile in width at its narrowest jjoint. The bar is concave 

 westward and its outer end is attached to the west end of the rock cuesta. 

 The beach is built of sand and gravel and presents a broad, slightly ter- 

 raced slope to the west. The sands and gravels of which it is built have 

 been transported from the west along the shore. They were derived from 

 a series of low sea-cliffs cut chiefly in. interglacial sands and gravels. 



Back of the beacli is a series of sand dunes rising about 50 feet above 

 lake level. The dune belt is aboiit a quarter of a mile in width. The 

 greater portion of it is stationar}', but in a few places the sand is slowly 

 ovenvhelming the marshes and woodlands which lie east of it, on the 

 earlier built portions of the bar. The east side of the bar is overgrown 

 with marsli grasses and slopes gently down below the level of the water 

 of Presque Isle bay. 



Toronto island. — The harbor of Toronto is formed by a flying spit, 

 composed of gravel and sand, which lies about 2 miles offshore (at the 

 west end). The eastern end of the spit is connected with the mainland 

 near the eastern cit}' limits b}' a long, low, narrow bar. The length of the 

 bar and spit together is about 4i4 miles. At the western or free end 

 the gravels have been looped northward. 



