GIBRALTAR TUNNEL.

Matamata Record, Volume XIII, Issue 1104, 10 March 1930, Page 6

GIBRALTAR TUNNEL.

GEOLOGIST’S VIEWS. The Gibraltar tunnel may be an achievement of the 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 20 years ago, is one of Britain’s most widely travelled geologists. He is constrained to emphasise the difficulties of cutting a railway tunnel connecting the two sides of the Pillars of Hercules, though he points out that in many respects the 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 economic problems, such as putting a French army into Africa, in the eveht of France and Spain being in alliance and needing troops to crush a North African insurrection. The difficulties which Professor Gregory foresees are geological in origin. • Whereas the land which would be traversed by a Calais-Dover tunnel is of soft chalk,, that, below the 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 been overturned. The sea in the strait is 2000 to 3000 feet deep. To find a line where the ocean is level is less than 1500 feet 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 tunnel far longer than the eight miles separating Tarifa from the Moroccan coasts c If an eight miles tunnel began at sea level and reached a deptlvof 1500 feet in four miles, the gradient would be one in fourteen. To reduce the gradient" to J one in twenty-eight—and this would! be 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 20 miles long. The geological history of the area is almots 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 belts of broken, fissured rock, which may well.. gj,v& serious trouble before the tunhel'flPjr made watertight. In view of th»r cost of the Mersey tunnel, now being: constructed between Liverpool and Birkenhead, Professor Gregory regards the estimated cost of the Gibraltar tunnel —£10,000,000 —as unduly? optimistic. As he says, the earths movements which opened the Pillars* of Hercules to shipping left condb- , tions unfavourable to the construction of a railway canal. ..