265 



Unmanured — 1912: 56.38 bushels, 4.72 cwt., 11.94 bushels per 

 cwt. 1913 : 59.81 bushels, 6.78 cwt., 8.81 bushels per cwt. Total 

 and average, 116.19 bushels, 11.50 cwt., 10.10 bushels per cwt. 



The difference in the bushel-Weights of the manured and un- 

 manured coffee should particularly be noticed. — Monthly Bul- 

 letin. 



AN INTERESTING LETTER CONCERNING OAHU'S 

 GEOLOGY. 



The College of Hawaii. 



Honolulu, Hawaii, Sept. 29, 1915. 



Editor Hawaiian Forester and Agriculturist. 



Dear Sir : — I think that Forester readers will be interested in 

 this hitherto unpublished letter by the late Doctor Sereno E. 

 Bishop concerning geological formations on Oahu. The letter 

 was made available to me through the courtesy of Mr. Merry- 

 mon, at the U. S. Magnetic Observatory, Ewa. 



Very truly yours, 



Vaughan MacCaughey. 

 Honolulu, January 18, 1915. 



Mr. S. A. Deal, U. S. Magnetic Observatory, Ewa, Oahu. 



Dear Sir: — Your letter is before me asking "for information 

 concerning the coral plain forming the southwestern part of this 

 island." 



I cannot claim much knowledge of the science of geology, but 

 many facts peculiar to the structure of the rocks, mountains and 

 shores of these islands have engaged my attention. 



I will try to state such information as I possess in respect to 

 "the depth of the coral, its method of formation and elevation, 

 probable age," etc. Also I will state the theory of the subject as 

 it has taken shape in my own mind, very probably not materially 

 differing from that of others. 



The island of Oahu is composed of two separate masses of 

 volcanic mountains, the eastern or Konahuanui, or Koolau moun- 

 tain, slightly encroaching on its older sister, the Waianae moun- 

 tain, at the southern extremity of which stands your observatory. 

 Both mountains are of great antiquity, evidenced by the enor- 

 mous erosion or weathering which they have undergone. This 

 slow gnawing away by the rain storms has largely obliterated the 

 original dome-form of these piles of lava-flows whose strata lie 

 exposed in the numerous deep ravines. The only remaining 

 traces of the original dome-surface are the short slopes of the 

 foothills which survive on the west side of the Koolau range, and 

 a very little on the SE. flank of the Waianae mountain. What 

 remains of both mountains are the skeleton ridges and pinnacles. 



