IN THE DEGRADATION OF THE LITHOSPHERE. 391 



evident after an inspection of that portion of the waters and land 

 masses along the Gulf of Maine. The positions of this group have 

 been plotted by drawing lines connecting the greatest numbers of 

 the islands including reefs which are regarded as islands. While 

 the distribution of these islands is not so striking as the islands of 

 Casco Bay to the north and east yet it is apparent that the appli- 

 cation of the repeating pattern establishes here the existence of a 

 fairly regular system of jointing which may be stated to control 

 the position of this group as a series of upstanding residues of 

 erosion from an older land surface, a small illustration of the more 

 widely known case of the British Islands as remnants of a former 

 series of connected structures all part of the mass of the continent 

 of Europe. 



With this plotting of the Shoal Islands may be compared the 

 plotting of the positions of the Canary-Madeira group. I have 

 used for this the map from C. GageP^ in his discussion of the 

 islands of the middle Atlantic. (These were shown by lantern 

 slides while reading paper.) The arrangement of practically all of 

 these Atlantic islands shows lines of a parallel grouping so very 

 similar to the development of continental volcanic vents and fis- 

 sures along lines of separated segments or joints that it will hardly 

 be disputed that the same principle has worked in each case. These 

 islands consist in part, according to Gagel, of volcanic cones built 

 up from the floor of the sea and in part are "broken remnants of 

 the European-African continent. "*° 



According to Gagel three of the Canary group, namely La 

 Palma, Fuertaventura and Gomera " show the undoubted represen- 

 tatives of very old volcanic, archean and sedimentary formations, 

 which form the true sockets (=Sockel) of the islands and prove 

 themselves to be part of an old great continent, whose shattered 

 fragments still appear in these islands." The other islands of this 

 group consist of recent volcanic eruptives of Tertiary or Quater- 

 nary age carrying in some instances portions of marine Tertiary 



39 C. Gagel, " Die Mittelatlantischen Vulkaninseln," in " Handbuch der 

 Regional Geologic," Vol. 7, part 10, Heidelberg, 1910, pp. 1-32. Here will be 

 found the literature for this group noted and original references given. 



■i'> Op. cit., p. 31. 



