COMPARISON OF ANCIENT AND MODERN SHORES. 



73 



In the formation of beaches there is a tendency to straighten crooked 

 coast-lines by the construction of bars iu front of inlets, which are thus con- 

 verted into bays or lagoons. Burlington bay, at the western end of Lake 

 Ontario, is an illustration. Here, a narrow beach (fig. 5) cuts off a bay five 

 ►miles long, whose depth is considerable, reaching to 78 feet. This is a particu- 

 larly well-chosen example, for at the head of the bay there is a spit — named 

 Burlington heights (Ji, fig. 5), rising to 108-116 feet above the lake — 



Figure 3. — Section showing the Floor of a Cut Terrace without Beach but with Boulder Pavement. 

 P= Boulder pavement. W= Old water-level. 



cutting oft" an older bay, now represented by the Dundas marsh. This spit, 

 when the waters were at its level, formed a portion of an ancient shore (to be 

 described in a future chapter) in the same manner as Burlington beach 

 forms a portion of the modern lake-shore. 



Figure 4.— Section showing a Cut Terrace with a fragment of Old Beach partly concealed by a Landslide- 



6 = Boulder pavement. c = Fragment of old beach, d = Drift. s= Landslide, iv = Old water- 

 level. 



In places, where the waves break upon the more exposed coast, the beaches 

 are apt to be piled up a few feet higher than their mean level. The oppo- 

 site result is seen where the ridges are fashioned as spits and pass below the 

 surface of the water in the form of submerged bars. The increase in the 

 depths of the water in front of the beaches is usually veiy gradual. 



The study of the modern and ancient shores is reciprocal. By the former, 

 still washed by waves, we can identify the latter ; and by the examination of 

 the floors iu front of the raised beaches, we can more fully understand the 

 action of waves upon the modern coasts, than where the subaqueous deposits 

 cannot be seen. The muds, derived from the encroachment of the waves upon 

 the land, are assorted ; the coarser materials being those which form the 



X-Bull. Geol. Soc. Am., Vol. 1, 1889. 



