INTRODUCTION. 



THE Solomon Islands cover an area 600 miles in length. 

 They include seven or eight large mountainous islands 

 attaining an extreme height, as in the case of Guadalcanar 

 and Bougainville, of from 8,000 to 10,000 feet, and possess- 

 ing a length varying from 70 to 100 miles, and. a breadth 

 varying between 20 and 30 miles. In addition, there are* a 

 great number of smaller islands which range in size from 

 those 15 to 20 miles in length to the tiny coral island only 

 half a mile across. The islands fall naturally into two 

 divisions, those mainly or entirely of volcanic formations 

 and those mainly or entirely of recent calcareous formations. 

 In the first division, St. Christoval may be taken as a 

 type of the large mountainous islands possessing massive 

 profiles, such as Guadalcanar, Malaita, Isabel, etc. St. 

 Christoval, which rises to a height of 4,100 feet above tlie 

 sea, is composed in the mass of much altered and some- 

 times highly crystalline volcanic rocks (such as, in their 

 order of frequency, dolerites, diabases, diorites, gabbros, 

 serpentines, and saussuritic felspar-rock) which, as I learn 

 from Mr. T. Davies, have been both formed and altered at 

 considerable depths and indicate great geological age and 

 extensive denudation. Recent calcareous rocks, such as 

 will be subsequently referred to in the description of the 

 second division of islands, flank the lower slopes at the sea- 

 border up to an elevation of 500 feet. Fragments of similar 

 diorites, dolerites, and other dense basic rocks, all much 

 altered and often schistose, have been transported by trees 

 to the coral islets off the jsoasts of Guadalcanar and afford 

 evidence of the. geological structure of that island. Serpen- 

 tines were obtained by Dr Hombron in 1838^ from St. 

 George's Island, which is " ipso facto " a portion of Isabel. 

 Bougainville and New Georgia are largely of more recent 

 origin, as is indicated by their numerous symmetrical vol- 



' '- Voyage au Pole Sud ct dans L'Oceanie," (D'Urville). Geologie : 

 part ii., p. 211. 



