434 THE POPULAR SCIENCE MONTHLY. 



UPS AND DOWNS OF THE LONG ISLAND COAST. 



By E. LEWIS, Jk. 



" Daily it is forced home on the mind of the geologist that nothing, not even the wind 

 that blows, is so unstable as the crust of this earth." Dakwin, in 1835. 



OBSERVATIONS made around the shores of Long Island justify 

 the conclusion that they have undergone important changes in 

 time geologically recent. These changes appear to have arisen from 

 a series of vertical movements, by which the coast has been alter- 

 nately elevated and depressed. 



In consequence of these movements the shore-line of the island 

 has advanced and again receded, perhaps, in repeated instances : 

 being at one time, upon the ocean-side, from fifty to seventy miles 

 southward of where the waves now break; while at another period 

 the highest hills of the island were largely if not wholly submerged. 

 The persistence and extent of these movements are interesting and 

 important questions in geology. We do not know at present how 

 great the oscillations of the coast may have been, but enough is 

 obvious, in the records they have left in the contour and structure 

 of the island, to show that they have been much greater than is 

 indicated on the adjacent mainland of Southern New England. We 

 shall endeavor to follow these records, obscure and perplexing though 

 they sometimes are, back to the period in which Long Island may be 

 said to have had its origin a period which witnessed the approach 

 and presence of a great ice-sheet upon this coast. 



It is not questioned, we believe, that Long Island is a terminal 

 glacial moraine, and that the material of which it is composed is the 

 debris of regions over which the ice moved in its progress toward the 

 sea. Its underlying portions are beds of laminated sands and clays 

 which have been referred to periods antecedent to the advent of the 

 ice, and which constitute in one sense a part of the island. Its 

 great mass, however, overlies these beds, and presents two general 

 forms of structure. One is known as the " unmodified bowlder-drift," 

 in which there are no stratified beds; the other is the "modified 

 drift," or that in which the material has been distributed in layers 

 chiefly by the action of waves. Much of the hill-region of the island 

 presents the peculiar pell-mell structure of the one the stratified 

 gravels and sands of Southern Long Island are typical of the other. 

 These differences in structure, and other facts to be mentioned, imply 

 great changes in the relative level of land and sea upon the coast. 



In considering these movements of oscillation it will be convenient 

 to notice the latest first, and others in their order. A persistent 

 invasion of the ocean upon the shores of the island has taken place 



