BIRDS OF ESSEX COUNTY. 3T 



either end, so that they describe the arcs of circles, and resemble a series of 

 gigantic amphitheaters. One of these waves can easily be traced for some 1350 

 yards, or three quarters of a mile, stretching from the salt creek on the inside 

 to the sea on the outside. The breadth of the waves varies from 40 to 200 

 yards, and the height from 20 to 50 feet. The highest points or peaks gener- 

 ally have long ridges of sand to leeward of them towards the south, exactly the 

 same formation as seen in snowdrifts. Every now and then there is a cross-valley, 

 sloping gently upwards with wind-swept perpendicular sidewalls. Everywhere 

 in cuttings on the sharp faces, the wind stratifications are visible, and are 

 interesting for study. The strata generally dip slightly towards the south as 

 the sand is left by the wind on the southern or leeward slope of the dunes, but 

 they vary greatly and are irregularly superimposed. Their characteristics are 

 brought out more strikingly by the wind cutting deeply into the loose strata 

 leaving the compact ones in bold relief. The ripple marks made by the wind 

 and at right angles to it on the surface of the dunes constitute another inter- 

 esting feature. 



The dunes are restrained in their career by the binding power of the 

 beach-grass {Ainnwpkila arunditiacca), whose roots e.xtend in a network through 

 the sand. These roots are exposed on the windward or retreating side of the 

 dune and hang in festoons. On the leeward side, the grass struggles hard to 

 keep above the accumulating sand. As a rule, owing to the binding grass, the 

 changes in the dunes are slow. When the sand succeeds in breaking away from 

 the grass, or in covering it up faster than it can push its way through, the 

 dune sometimes advances with great rapidity, and a steep slope of soft sand is 

 formed to leeward, where it is suddenly dropped by the wind. Occasionally a 

 desert of several acres in extent of wind-swept sand, unhampered by grass, is 

 formed among the dunes. 



As illustrating the effect of the wind over a region devoid of binding grass, 

 there occurred during the severe winter of 1903-4 an immense drift of snow 

 and sand, separate and mingled, encroaching on the north side of a growth of 

 pitch pines in the Ipswich dunes. The snow was so protected by a layer of sand, 

 from one to two feet in thickness, which reflected but did not so easily conduct 

 the sun's rays, that the snow became compact and crystalline, in fact a miniature 

 glacier. On May 15th, 1904, this crystalline snow had a thickness of 38 inches 

 at its exposed face, under which, extending back to a distance of three feet, was a 

 true glacial cavern. The sand on top was cracked or crevassed, and this, 

 together with the bending of the trees, suggested a slight motion down the 

 slope. On May 30th, the face of ice was covered by sand, but marks made on 

 a white birch showed that the drift had sunk 42 inches since April 24th and 22 

 inches since May 8th. A tree released entirely from the snow and sand had 



