386 EHRENFELD— JOINTING AS A FUNDAMENTAL FACTOR 



planation at present in action along the New England coast. The 

 data mentioned are taken from personal observation of my own 

 and part from the published literature on the subject. Particular 

 reference may be made to the following sheets of the U. S. Topo- 

 graphic Folio, namely, Casco Bay, Portland, Booth Bay, Bath, 

 Penobscot and the following hydrographic charts, Nos. io6, 107, 

 315, of the U. S. Navigation Bureau, and also the U. S. Coast 

 Pilot,^^ for details as to soundings, situation of reefs, bars, islands 

 and harbors. It is not necessary to give the details of this. 



The shore of the coast of Maine is almost a continuous succes- 

 sion of rocky points, entrant bays, steep cliffs, or outlying islands 

 and reefs, all connected more or less by sand bars, sand dunes, 

 necks, tidal flats or by back lying marshes. Out beyond the actual 

 shore or strand line lie in addition successions of islands, reefs and 

 rocky points, these all practically being composed of the same sort 

 of rock as that exposed along the shore and with some rare excep- 

 tions are not to be distinguished from the rock masses in connec- 

 tion with the mainland or shore line except by the fact that these 

 outlying masses are surrounded entirely and continuously by sea 

 water. The topographic features about Portland Harbor and Casco 

 Bay will illustrate sufficiently these various features. The most 

 marked feature of Casco Bay is the extraordinary number of 

 islands, rocky points and reefs which, as may be seen in the various 

 publications referred to, are arranged in a general parallelism and 

 in a northeast-southwest direction. This direction is practically 

 the same as shown by the prevailing dip and strike of the rock 

 masses about this portion of the Maine coast. These Casco Bay 

 islands are so eminently arranged in repeating patterns as to sug- 

 gest, even without the necessity of any actual plotting being done, 

 definite lines of joint control, the submerged reefs as may be seen 

 in the navigation charts are frequently continuations of the same 

 jointing structures. If the general lines of jointing and the pre- 

 vailing lines of strike be compared with some of the small islands 

 and necks near Portland Harbor, the general connected structure 

 of all is apparent. Thus, for example, at Prouts Neck, near Port- 



36 u. S. Coast Pilot, Atlantic Coast, Parts I., II., St. Croix River to Cape 

 Ann. Washington, 191 1. 



