DEPARTMENT OF MARINE BIOLOGY. 181 



materials are considerable and will be worked over to supply the details 

 necessary for the final report. A general sketch of the project may be pre- 

 sented, as follows: 



The island of Tahiti consists of two dist'nct high land masses connected by a 

 narrow, low isthmus. The larger mass, Tahiti Nui, or simply Tahiti, culmi- 

 nates in several sharp peaks, the highest of which, Orohena, is credited with 

 being 7,321 feet in altitude. The smaller mass, Tahiti Iti, or the peninsula 

 of Taiarapu, likewise culminates in several sharp peaks, the highest of which, 

 Roniu, is credited as being 4,341 feet in altitude. Both Tahiti Nui and Tai- 

 arapu are much dissected and give evidence of having suffered tremendous 

 and deep erosion, giving rise to deeply penetrating valleys with steep or even 

 vertical walls, separated by high, narrow, even knifeblade-like ridges. Both 

 land masses are more or less surrounded by a broader or narrower flat strand 

 formation, interrupted here and there by the lower ridges descending to the 

 ocean, and in several districts strongly cliffed. Both land masses are practi- 

 cally surrounded by reefs, fringing or barrier, awash or well submerged, but 

 passes through the barrier reefs are numerous, allowing access to the shore 

 either dii-ectly or by way of the broader or narrower, usually about 18 fathoms 

 deep, lagoon moat. Rivers, some of considerable size and force of water, 

 traverse the valleys, and the passes are fairly definitely situated relative to the 

 more considerable debris-carrying rivers. 



The reefs about Tahiti are both extensive and varied. A survey indicates 

 at least six types, each bearing directly on the general as well as on the 

 special problem of reef formation. The six reefs chosen for examination are: 

 (1) incipient reefs at Tahara Mountain in the Arue district; (2) incipient reefs 

 in the Papenu district; (3) exposed fringing reef at Arue in the Arue district; 

 (4) combination reef at Atiue in the Punaauia district; (5) typical protected 

 fringing reef at Auae near Papeete; and (6) the typical barrier reef outside 

 Papeete Harbor. 



Preliminary to reef study, an examination was made of the exposed outer 

 point of Tahara Mountain and certain portions of the Papenu coast which 

 are devoid of any conspicuous reef formation whatsoever. 



Tahara Mountain terminates seaward in a bold bluff of volcanic agglome- 

 rate, much decomposed and traversed by broad anastomosing dikes. About 

 the seaward face is a broad, flat shelf, a little above high-water mark, strongly 

 cliffed above and below. The waves dash over it with violence at times of 

 high water. The seaward cliff extends vertically downward for 4 to 5 fathoms 

 and beyond it, about 0.75 mile, reaches 12 to 14 fathoms, beyond which, 

 about a mile to the seaward, arises a submerged barrier reef to within 3 or 4 

 fathoms of the surface. Beyond the submerged barrier reef the coast slopes 

 suddenly, reaching 100 fathoms in the distance of 3 miles from the point, 

 whence the descent to 1,000 and more fathoms is abrupt. Studies at this 

 point indicate the possible existence of two wave-benches, one in the neigh- 

 borhood of the present sea-level and one submerged 20 to 30 fathoms. 



There is indication of similar conditions along the Papenu coast. Much of 

 this coast is of a coarsely columnar lava, at and below sea-level. There is 

 some, but not positive, indication of a narrow wave-bench at 12 to 20 feet 

 above sea-level, a narrow one at sea-level, and a broader or narrower one 20 to 

 30 fathoms below sea-level. The columnar structure of the rock of the cliffs, 



