MUSEUM OF COMPARATIVE ZOOLOGY. 159 



dam of sand at low stages of water, which is in its turn broken through 

 acain whenever sufficient head of water has accumulated behind it. 



Some extensive ancient dunes, from one hundred to one hundred and 

 twenty feet in height, indicate an effect of the trade winds now no longer 

 acting. It may be that some of these more ancient inland dunes, which 

 have become solidified near Diamond Head, were formed under the influ- 

 ence of the trades before their full force on the eastern edge of the reef 

 was destroyed by the elevation of the long hill forming Diamond Head. 

 It may be that we owe to the presence of these dunes most of the coral 

 sand and calcareous material which we find up to a considerable eleva- 

 tion between Diamond Head and Honolulu in the Manoa Valley. 



Although the Honolulu reef has a far less rich fauna than the reef of 

 Kahului Bay, yet the limestone which it forms, not having been exposed 

 to the action of the trade-wind surf, presents the reef much as we see it, 

 flourishing and gradually dying out in proportion to its proximity to 

 the shore. The corals, Serpulce, NuUipores, echinoderms, mollusks, and 

 even Crustacea, are not ground to pieces, as in reefs open to the violent 

 action of the sea, where all traces of their identity are destroyed in the 

 process of formation of the coral limestones characteristic of such ex- 

 posed reef shores. On the contrary, the coral heads themselves, as well 

 as all the animals flourishing upon such a protected reef as that of Hon- 

 olulu, are rapidly fossilified and imbedded in limestone, being gradually 

 covered with the floating lime held in suspension or in solution in the 

 water ; so that, whenever we get a good section of the shore coral lime- 

 stone, we invariably find, either on the reef-flat itself, or on the imme- 

 diate shore line, or on those portions of the reef which have been slightly 

 elevated, a limestone representing the reef as it grew and flourished, in 

 which we can plainly distinguish the different species of coral, as well as 

 the invertebrates which once lived in their shelter. 



In the section to be seen on King Street, near the Prison Point, be- 

 yond the bridge, a face of about six feet in height was being quarried, 

 the highest point perhaps three feet above high-water mark, the Prison 

 Knoll, which is the continuation of this limestone ridge, being about ten 

 feet above high-water mark. This and another limestone knoll facing 

 the opening of the Nuuanu Valley are formed of a close white lime- 

 stone mass of decomposed reef rock, in which the individual heads are 

 more or less distinct, and which contains a large number of shells and 

 echinoderms imbedded in the mass cementing the corals together. The 

 western and eastern extensions of this old shoi'e line of the reef, which 

 must have been elevated about twenty feet above the sea level, has been 



