BULLETIN OF THE UNITED STATES FISH COMMISSION. 4,')1 



Cod. It cannot be assumed to be a fold of strata on the Appalachian 

 system, because these strata have a southwest and northeast direction. 

 A look at the map of Cape Cod shows that this coast is subjected to the 

 visitations of powerful northwest and northeast winds, which roll up 

 sand dunes a hundred feet high. If we furthermore mention the cir- 

 cumstance that the tidal currents which run into and out of Massa- 

 chusetts Bay make right across the bank, we have named two agents 

 which work at its destruction. Its existence in its present shape and 

 depth of about 10 fathoms as a submarine bank is largely due to the 

 protection afforded by Cape Ann aud Jeffrey's Ledge on the northward 

 and by Cape Cod on the southward. 



The Massachusetts Coast. — The coast of Massachusetts assumes 

 a distinctly rocky appearance about Scituate and maintains this charac- 

 ter to beyond Cape Ann. According to Professor Hitchcock (Smiths 

 Cont., Vol. IX), Boston Harbor has been scooped out of softer meta- 

 morphic slates by the action of tides and breakers, whilst these agents 

 had no perceptible influence upon the unyielding syenite of Cape Ann 

 and Cohasset. 



Jeffrey's Ledge. — Jeffrey's Ledge, off the coast of New Hampshire, 

 lies in direct continuation of Cape Ann, and extends in a direction 

 parallel to the ranges of hills composing the cape. This ledge presents 

 a veiy different appearance from the banks heretofore considered; it is 

 much bolder, and instead of a large and nearly level surface, as possessed 

 by George's Bank and Stillwagen's Bank, it shows a narrow ridge, rap- 

 idly falling off east and west into depths of over one hundred fathoms. 

 This shape points to subterranean upheaval as the cause of its forma- 

 tion, and we conclude that it is the continuation of Cape Ann and identical 

 with it in its geological structure; that its body consists of granite and 

 syenite. The difference in level, Cape Ann being about 250 feet above 

 and the ledge 90 feet below the ocean, is inconsiderable in a geological 

 view. It is a characteristic feature of this one and nearly all the other 

 ledges in the Gulf of Maine that their surface is covered by a fine sand, 

 which changes into a coarser sand and gravel on their sides, which in 

 turn are lost under a thick covering of mud when we get into the deeper 

 parts of the gulf. 



The New Hampshire Coast. — Between Cape Ann aud Hampton 

 River we meet alluvial deposits, but thence to beyond the limits of New 

 Hampshire, to Cape Small, in Maine, we find stratified rocks, which may 

 be designated as metamorphic slates (principally mica schist) with nu- 

 merous irruptions of granite and trap. Cape Elizabeth aud the islands 

 in Casco Bay belong to this formation. According to the soundings it 

 extends a considerable distance into the sea and includes the Isles of 

 Shoals, Boon Island, and the ledges off Portland Harbor. The strike of 

 the strata is uniformly northeast, and the peculiar tendency of this region 

 is the formation of low and parallel ridges of hills and islands above the 

 water aud of submarine rocky ledges running northeast. Cape Eliza- 



