PHYSICAL OCEANOGEAPHY OF THE GULF OF MAINE 895 



In weighing the significance of drifts of this sort, when bottles are set out so 

 close to land, due consideration must be given to the stage of the tide. In this 

 instance all the bottles that showed a drift toward the north were set out on the flood 

 tide, so that they must have traveled up the bay at first. Consequently, the fact 

 that they stranded where they did indicates a predominance of ebb over flood, or 

 in other words, a drift out of Cape Cod Bay along the eastern side. 



Before leaving the bottle drifts in Massachusetts Bay, I should emphasize the 

 fact that not one of them is clockwise, but that all can be safely interpreted anti- 

 clockwise within the bay or from north to south across its mouth and so down past 

 Cape Cod. 



At first sight the evidence (by bottle drifts) of a dominant set out of Cape Cod 

 Bay around Cape Cod, and so southward along the outer shore of the latter, might 

 seem contradicted by the physiography of the cape; for, as Davis (1896) has shown, 

 the so-called "Province lands," which form its tip, were built up by the transference 

 of sand along shore from the south. In fact, the existence of the sand spit known 

 as Wood End, which incloses Provincetown Harbor on the southwest, is sufficient 

 evidence of beach-drifting inward toward the bay, not outward from the latter, as 

 the bottle drifts demand. However, this apparent contradiction vanishes on closer 

 analysis. Beach-drifting" is effected chiefly by the longshore component of wave 

 action. 



A glance at the chart will make it clear that winds from the only direction 

 (between north and southeast) that can drive a sea against the tip of the cape heavy 

 enough to move much sand necessarily produce a wave current westward around 

 its extremity. This would be the case even if the cm-rent a few hundred yards out 

 (tidal or not tidal) were making in the opposite direction, perhaps carrying our drift 

 bottles with it. Neither the tidal nor the nontidal currents scour the shore line here 

 violently enough to be of more than minor importance.'* 



Thus, beach drifting may be constantly in one direction, but the dominant set 

 of the water as constantly the opposite only a short distance out at sea; and it seems 

 sufficiently established that this is the case at the tip of Cape Cod. 



Farther south along the cape beach-drifting acts in the same direction as the 

 nontidal drifts, both making to the southward. 



The drifts from series O (set out near the coast, about midway between Cape 

 Ann and Cape Elizabeth, on July 18, 1926, by T. E. Graves) proved consistent with 

 these Massachusetts Bay drifts (as, also, with the drifts from the Bay of Fundy in 

 1919) for the three recoveries so far reported were all from the southward — two from 

 Cape Ann and the other from the north shore of Massachusetts Bay at Salem. 



DRIFTS OF BOTTLES SET OUT OFF CAPE ELIZABETH AND OFF MOUNT DESERT 



The drifts so far discussed have proved so consistent, both regionally and from 

 year to year, that the type of circulation which they represent may safely be taken 

 as characteristic of the southern and southwestern parts of the gulf. The drifts of 

 bottles put out off Cape Elizabeth and Mount Desert have proven equally consist- 

 ent among themselves, though interpretation has not been so easy. 



" Johnson (1919 and 1925) has proposed this convenient term for the longshore transference of sand or other debris. 

 " For an illuminating discussion of the relative importance of wave and other currents in causing beach-drifting, see lolmson 

 (iei9; 192S, p. £0S). 



