THE GIBRALTAR TUNNEL

Evening Post, Volume CIX, Issue 36, 12 February 1930, Page 19

THE GIBRALTAR TUNNEL

EXPERT'S OPINION : The Gibraltar tunnel may be ;an achievement of tho next • generation, comparable with the cutting: of. the Panama and Suez Canals in the ;two previous generations. The colonisation' of Northern Africa by France, Italy, and Spain has given the project |new | importance. It is therefore interesting to have the opinion of a recognised geological expert upon it. Professor J. W. Gregory, of Glasgow, who was director of geological! survey in Victoria some twenty years ago, is one of Britain's most widely travelled, geologists, writes the London correspondent of the Molbourne "Argus." He is constrained to emphasise the difficulties of cutting a railway tunnel connecting the two sides of the Pillars of Hercules, though ho points out that in many respects tho project is' tempting. Only eight miles of sea separate Spain from the Moroccan coast, less than half the distance between Calais and Dover. Moreover,, the tunnel would solve some difficult military and econo-1 mic problems, such, as putting a French army into Africa, in the event of France and Spain being in alliance and needing troops to crush a .North African insurrection.

Tho difficulties which Professor Gregory forsees are geological 'in origin. Whereas the land which would be traversed by a Calais-Dover tunnel is of soft chalk, that below tho Straits of Gibraltar is of hard mountain rocks, which are steeply tilted, and have been so broken that the limestone of the Rock of Gibraltar has actually teen overturned. The sea in tho strait is 2000 to 30.00 feot deep. To find a line where the!ocean level is less than 1500 feot, the tunnel would have to be cut some miles west of Tarifa, where the strait is wider. As Professor Gregory points out, the effect of this depth upon the railway gradient is serious. Indeed it necessitates a tunsel far longer than the eight miles separating Tarifa from the Moroccan coaut. If an eight miles tunnel began at eea level and reached a depth of 1500 feet in four miles, the gradient would bo one in fourteen. To reduce the gradient to one in twenty-eight—and this would bo steep for a railway—the length would have to be increased to 16 miles. Professor Gregory says that, unless the rackwork used on mountain railways is introduced, the Gibraltar tunnel will have to be not fewer than, twenty milea long. . The geological history of tho area Is almost as interesting as the engineering problem. Probably the deep basin is due to the sinking of the sea floor between fractures of the crust* These fractures, doubtless, traverse the whole of the strait, and they have; formed bolts of broken, fissured rock, which may well give serious trouble before the tunnel is made watertight. In view of the cost of tho Mersey tunnel, now being constructed between Liverpool and Biikcnhead, Professor Gregory rogards tho estimated cost of thf. Gibraltar tunnel—£lo,ooo,ooo—-as unduly optimistic. As he says, the. earth movements which opened the Pillars of Hercules to shipping left conditions unfavourable to the construction of a railway canal. .:,■■' . . :