SCIENCE 



IStEW YORK. FEBRUARY 10, 1893. 



THE ICE-WALL ON THE BEACH AT HULL, MASSACHU- 

 SETTS, JANUARY, 1893. 



BY J. B. WOODWOBTH, SOMERVILLE, MASS. 



The exceptionally long-continued cold of the early part of .Jan- 

 uary, this year, favored the development of a considerable w/all 

 of coast-ice on the long barrier beach connecting the rocky head- 

 land of Nantasket with Strawberry Hill and the neighboring 

 drumlin at Point Allerton at the entrance to Boston Harbor. At 

 the same time, the embayed waters of Boston Harbor froze over. 

 I visited the beach at Hull on the 24th of the month, at a time 

 the temperature had risen above the freezing jjoint, and when the 

 sheet ice had left the shore and was only visible as cakes floating 

 near the horizon. 



At Nantasket, from the vicinity of the cafes northward to 

 near Point Allerton, the ice-wall formed a rampart near high- 

 tide mark of triangular cross-section, having an average elevation 

 of about 8 feet and a breadth of base of 20 feet. The seaward 

 slope of this wall was shorter and steeper than the landward, and 

 was also much more irregular, owing to the action of the waves 

 and some melting. The landward slope merged into the sheet 

 of snow back of the beach. The accompanying diagram will 

 make clearer this description. 



Fig. 1. — General eross-sect'ou of the Ice-wall al Hull. 



The wall was composed in part of cakes, but in larger measure 

 of granular ice, making the whole a compact mass, whose front 

 was broken at frequent intervals by recesses swept by the waves 

 at high tide. The beginnings of these recesses wore seen in 

 numerous caverns at the bottom of the ice, some of which were 

 large enough to permit a man to crawl under the arch, and in 

 one case a breach had been made through to the beach in the 

 rear of the wall. In another instance, where the crest of the wall 

 was low, the arch was fissured, as shown in Fig. 3, apparently by 

 the pressure of waves in passing through the tunnel. 



Pig. 3. — Ice-arch fissured by wave-action. 



From many of the smwll c^ves little streams were trickling out 

 over the sand beach in front. These streams were busily em- 

 ployed at low tide in building and re-arrat)ging small deltas of 

 fine sand, a long stretch of which lay between high and low tide- 

 marks. 



The drainage of water produced by the superficial melting of 

 the ice at mid-day was mainly in the form of drops from the 

 protuberant masses one or two feet above the base, which was 

 slii^htly receding, a feature determined by the water at high tide. 

 These drops of water fell upon the wet sand of the beach and 

 made well-marked pits, the cross-sections of some of which are 

 shown in the adjoined Fig. 3. These pits were distributed along 

 the front of the ice-wall ju^t under the high-tide limit. 



Some of these depressions resemble the so-called rain-drop im- 

 prints on the older strata, and serve to make us cautious in the 

 interpretation of such markings. I have also seen the spray from 

 surf, as on the beach at Gay Head, Mass., make similar impres- 



sions. The larger impressions at Hull were as much as three 

 inches in diameter, but correspondingly shallow, while those 

 which were in process of formation were not over half an inch 

 across and half an inch deep. Around each pit, into which water 

 was dropping, a rim of sand was raised. The larger pits, just de- 

 scribed, were, except for what I am about to describe, without 

 any signs of the cause of their formation. In several instances, 

 however, I observed that water was dropping in a narrow, deep 

 pit, formed exactly in the centre of one of the large shallow ones. 



Fig. 3. — Pits made on the beach by water dripping from coait-ico. n. Deep 

 and narrow pit. b. Broad, shallow pit. c. Renovated pit. 



The explanation of these pits seems to be thi.--. that, after the 

 dropping has ceased for a time, as by the freezing of the surface, 

 of the ice-wall at night, the sands about the deep pits cave in, 

 being highly mobile by reason of the water they contain. If now, 

 on the next period of melting, drops of water drip from the same 

 icicle-like projection of the ice- wall, a new, deep, but narrow pit 

 will form in the place held by the old one. The geological inter- 

 est of these pits is evident when we compare them with some of 

 the pit-like depressions found in the Cambrian and other deposits 

 of beach origin. The surface of the arenaceous slates of pre 

 sumablv Lower Cambrian age in Somerville, Mass., are marked 

 with pits closely resembling many of these made by water falling 

 from coast-ice. In fact, it would be difficult to distinguish them 

 from the so-called genus of worm-burrows, Monocraterion, where 

 the long tube penetrating the sand is obscure or wanting. 



The strength of the waves applied to the face of this wall of 

 ice can be estimated from the fact that a whale, about 40 feet 

 long (Physeter macrocephalus), had been washed ashore abreast 

 of Strawberry Hill, and lay with his head to the north, close up 

 to the foot of the wall of ice, apparently in a position determined 

 by the run of the shore-current during a •'north-easter." The 

 depth of water necessary to float this body in was in part obtained 

 through the backing-up of the waves against the wall of ice. The 

 effect of this action on the regimen of the beach was better shown 

 on the bouldery pavement near Point Allerton. 



Under the ordinary summer conditions of this beach, the swash 

 of the surf advances up it as a thin sheet of foaming water, halts 

 for an instant, and then recedes, to be overtaken by another 

 wave. The ice-wall, however, at high-tide mark, or just below 

 it, interferes with the action of the swash. The result is that the 

 water is held up against the ice-wall, and when it recedes goes 

 out as a deeper sheet than when the wave has a chance to run up 

 the beach and spread out as a thin layer of water. This thin 

 sheet of water cannot move the larger boulders except by remov- 

 ing the finer materials from their bases, but the thick sheet in 

 front of the ice- wall acts more potently on the larger cobbles and 

 bouldei-s, dragging them up and down the beach, so that its aspect 

 is for the time quite altered. To this action must be added the 

 effect of cakes of ice, with inter-stratified layers of sand and 

 gravel and occasionally included cobbles, which are left pell mell 

 on the beach with the receding tide. 



The larger beach pebbles, which have been reduced to the form 

 of wear characteristic of their class, exhibit an interesting fact 

 which should be noticed here. During the season of minimum 

 wave-action, the pebbles are smoothed by attrition with the 

 finer gravels and sands, which are alone in movement; but in the 

 winter, during heavy storms, the pebbles and cobbles are dashed 

 together, and their smooth surfaces scarred with dents. In the 

 case of an elongate cylindrical pebble, it was very apparent from 



