zoo PEOF. E. HULLj LL.D., ETC., ON THE SUB-OCEANIC 



EXPLANATION OF PLATES. 



Plate I. 



These plates are taken by photographic process from the Admiralty 

 charts — on which I have drawn the isobathic lines of 200, 500, 1,000 and 

 1,200 fathoms — the first and last of which nearly coincide with the upper 

 edge and base of the Great Declivity (or Escarpment) which separates the 

 Continental Platform from the abyssal region of the ocean. It will be 

 observed how the Declivity is deeply trenched by valleys or " caiions " 

 running for greater or less distances into the Continental Platform — which 

 has a breadth of about 150 miles along the north-east coast of the bay. 

 Through this Platform, the deep submerged channels of the Loire, the 

 Gironde, and the Adour, may be traced by means of the soundings for 

 greater or less distances ; that of the Adour through its whole extent of 

 100 miles.* Along the north coast of Spain, the Platform is very narrow ; 

 but is deeply trenched by river valleys which can, with much certainty, 

 be connected with existing streams descending from the Cantabi'ian High 

 lands ; amongst these the caiion of the Caneira is the most distinct ; but 

 there are others on a smaller scale entering the Channel of the Adour. 



Plate II. 



In Plate II, the Platfoim is continued, and breaks oflF generally along 

 the 200 fathom contour — which is trenched by numerous channels which 

 can, with more or less certainty, be connected with the existing streams 

 of the mainland of Spain and Portugal. The caiions of the Lima, Douro, 

 the Mondego and the Tagus are clearly traceable ; but there are several 

 well-defined and very deep canons which trench the Great Declivity and 

 the Platform, but which cannot be very clearly referred to existing 

 streams ; one of these I have called " the Grand Canon " in lat. '49° 30' 

 traceable for 40 miles, and bounded by precipitous cliffs about 5,000 feet 

 in height on the south side. Another short, but very deep canon occurs 

 in lat. 40" 80' bounded by precipitous cliff's of about equal height with 

 that of the Grand Canon — which ojjen out on the abyssal region of the 

 ocean at the foot of the Great Declivity. 



The submeiged valley of the Tagus, with its remarkable Double Canon, 

 is admiiably defined by the soundings, and can be clearly traced from 

 its ancient embouchure up to within about ten miles of the mouth of the 

 existing river, where the channel becomes choked up by sand and silt. 

 It has an entire traceable length of 50 miles by one channel, and of 

 60 miles by the other. The Continental Platform along this coast has 

 an average bi'eadth of about 35 miles. 



* A plan of the sub-oceanic channel of the Adour on the scale of the 

 Admiralty chart is published in the Oeographical Journal, March, 1899. 

 The small figures on the maps and sections are fathoms— but unfortunately 

 they are in most cases too minute to be legible. 



