304 GUILCHER [chap. 13 



separated by a body of water more than 50 fm deep. A submarine scarp is 

 found at the outer edge of the islands, which resemble the shahan near Lith 

 exce])t for their emersion. Tiran Island, at the opening of the straits, bears a 

 beautiful series of uplifted terraces. Here we are deahng with one of the most 

 faulted areas in the world. 



Data are much more accurate for the continental borderland of Southern 

 California [Fig. 10 (c2)]. According to Emery (in Bourcart, 1950, and 1960), this 

 area, which includes deep, steep-sided troughs with intervening ridges, "may 

 have been a geosyncline during the Jurassic period, but most of it was uplifted 

 to form a broad land during the Cretaceous, Eocene and Oligocene. Erosional 

 bevelling followed by a downwarp allowed the region to be covered by epi- 

 continental seas during the Miocene. Near the end of the Miocene Epoch, the 

 region became blockfaulted, so that, from the beginning of the Phocene to 

 the present, deep basins were separated by high areas that constituted islands 

 and banks". The basins near the continent have been filled up by sediments, 

 whereas in those lying farther offshore the sedimentation proceeded at a much 

 slower rate. As seen above, Pleistocene submarine terraces occur on banks and 

 around islands (Emery, 1958). After these terraces were cut (probably in Wis- 

 consin times), they were warped, since a correlation diagram shows that each 

 of them is deeper around offshore islands and banks than off the mainland, the 

 differences in depth reaching about 225 ft. The average warp of the shelf edge 

 is about 160 ft per 100 miles. The formation of the features of this continental 

 borderland thus involves a number of factors : Mesozoic and Cenozoic sedimenta- 

 tion, subaerial planation, block-faulting, recent marine planation and deposition 

 and regional warping. But the main features, namely the basins and ridges, are 

 related to block-faulting. 



The banks between the British Isles, Porcupine Bank and the Faroes, which 

 may be considered as the continental borderland of North-west Europe, seem 

 to belong structurally to the volcanic belt of the North Atlantic, extending 

 from the Antrim Plateau to Greenland across Iceland. It is not possible to 

 ascertain if they were initially tied together into a single platform and separated 

 by further faulting, or if they were built as distinct units ; consequently, their 

 classification into a definite type remains doubtful. The seamounts on the slope, 

 such as those shown in Fig. 7, are Ukely to be submarine volcanoes in a 

 luimber of cases or salt domes in some areas. 



E. The Fissured Type (Fig. lOd) 



The fissured type consists of shelves in which a long and deep depression 

 runs parallel to the direction of the coast, dividing the shelf into an inner and 

 an outer part. Sometimes more than one depression of this kind is found. As it 

 has been shown above (Figs. 3 and 4), this type is common in glaciated areas : 

 Norway, Scotland, Labrador, South-east Alaska, Ellesmere Island, South-west 

 Greenland, West Spitzbergen, East Antarctica (H. Holtedahl, 1958; idem, in 

 Bourcart, 1959; Jivago and Lissitzin, 1957). It combines generally with deep 



