Marshall. — Geolor/// of Moorea and Rurutu /stands. 281 



Art. XXXVIII. — Notes on the Geology of Moorea and Rurutu Islands. 



By P. Marshall, M.A., D.Sc, F.R.G.S., Professor of Geology, Otago 



University. 



[Rend before the Otago Institute, 4th November, 1013.] 



The island of Moorea, or Eimeo, appears to have been first visited by 

 Captain Cook in the year 1777, though it had been discovered by Captain 

 Wallis ten years previously, and named by him Duke of York Island. 

 Cook anchored in the harbour called by him Taloo, on the northern 

 side of the island. This harbour is now called Papetoai, while another 

 similar bay, also on the north side of the island, is often called Cook's 

 Bay, though the great navigator never actually took his ships into it. 

 Though Cook did not visit the island before 1777, he had during his first 

 voyage sent one of his boats, under the charge of Lieutenant Gore, to make 

 observations on the occasion of the transit of Venus in 1769. Cook him- 

 self made similar observations at Point Venus, in Tahiti. Lieutenant Gore 

 reported that he had been well received by the Natives, though he regarded 

 the island as not very fruitful. 



Apparently the next vessel to visit the island was the ship " Duff," 

 under the charge of Captain Wilson, during the missionary voyage to the 

 South Seas. A plate showing the appearance of Taloo Bay is given on 

 page 83, " Missionary Voyage to the South Seas " (Wilson, 1799). 



In Cook's Voyages the rocks are said to be bluish, with little particles 

 of mica. In Wilson's Voyage the only reference that I can find to geology 

 is the following : " The island appears to have suffered great convulsions, 

 either from earthquakes or from other violent causes. Most of the hills are 

 high, with broken rugged sides, particularly about Taloo Harbour, from the 

 entrance of which they have a very striking appearance." 



Ellis, in his "Polynesian Researches" (vol. 1, p. 18), says, "In the 

 varied forms its mountains exhibit, the verdure with which they are clothed, 

 and the general romantic and beautiful character of its scenery, this island 

 surpasses every other in the Georgian or Society Groups." 



These extracts give a vivid and an exact idea of the highly picturesque 

 appearance of the island. The remarkable effects of subaerial erosion in 

 forming the pinnacled peaks, the piercing shape of the aiguilles and the 

 precipitous sides of the valleys have excited the wonder and admira- 

 tion of all geologists who have visited these tropical islands of the Pacific 

 Ocean . 



As is the case in Tahiti, Rarotonga, and in all of the high islands of the 

 eastern Pacific, Moorea is entirely formed of volcanic rocks, but all indica- 

 tions of the form of the original volcano have been lost. The lava and 

 scoria slopes of the volcanoes have been cut up by the erosive action of 

 the tropical rains and torrents into steeple-shaped peaks, separated by the 

 most profound valleys, with sides so steep that they cannot be scaled. 



Moorea is triangular in shape, each side of the triangle being about 

 eight miles in length. It is surrounded by a continuous coral reef about 

 a mile distant from the shore, and on it islands are situated here and there. 

 It appears that up to the present time no detailed information has been 

 available in regard to the rocks of which it is composed. 



