438 Her. It. Ashing ton Bullen — 



mineral is staffelite, a fibrous encrusting' crystalline variety of calcium 

 phosphate. A comparison of this rock with other examples of 

 phosphorite with encrusting staffelite shows a high degree of 

 resemblance. 



" Coprolitic phosphorite, being amorphous and variable in com- 

 position, has no definite specific gravity, but as crystalline apatite 

 reaches up to 3 - 2, we may consider phosphorite to be perhaps 10 per 

 cent, lower, or about 2 - 9. Taking the specific gravity of the rock in 

 mass with a Walker's steelyard, a value of about 26 was obtained, but 

 this was obviously much too low, owing to air imprisoned in the 

 interstices. A piece of the rock was therefore broken up and 

 the crushed fragments placed in a heavy liquid. By this method, 

 using Klein's solution (cadmium borotungstate in water), the specific 

 gravity was determined with some accuracy to be 2'91. 



" The rock No. 1 may therefore be described as phosphoritic rock 

 with staffelite. Its origin may perhaps be accounted for by the 

 accumulation of the excrement of fishes or more probably of birds." 1 



In a second communication Mr. Gwinnell says that a confirmatory 

 test for phosphorus in the rock had been performed and shows the 

 abundant presence of phosphorus. He has thus proved the presence 

 of phosphorus by both dry and wet chemical methods, as well as 

 recognizing the phosphorus-bearing mineral by specific gravity and by 

 a number of optical properties. 



(2) The Crystal Cave, near Bailey Bay. — This cave has been opened 

 to the public within the last two years. As it is lighted by electricity 

 the dazzling beauty of the stalactites has not been spoiled by smoke. 

 It was discovered by the persistent selling by boys for some time of 

 stalactites of great purity and beauty but of unknown provenance. 

 The source of their supply was at last found out. They used to enter 

 down a natural sloping passage (now artificially closed) which had 

 also been the entrance for the numerous birds which left their 

 bones for the present race of naturalists to find and describe. 

 Mr. L. L. Mowbray is to be congratulated on the discovery of so 

 many avian skeletons and also of their feathers preserved in the 

 stalactite. The determination of these remains is being steadily 

 pursued, and geological science will soon be enriched by their accurate 

 description and diagnosis. 



The salt-water lake in the cave is called the ' Cahow ' Lake, in 

 honour of the bird, now extinct, which frequented the islands 

 300 years ago in great numbers, but was ruthlessly exterminated 

 about 250 years since, being hunted in the night. 2 



1 The second alternative seems to me to be the most feasible. It is difficult 

 to conceive such a hard rock being formed under salt water from such materials. 

 Such crystallization would more likely take place on land elevated above the 

 sea-level, where crystallization could go on at the base of guano beds. Solid 

 rock is not forming under the sea at the present day. Wherever the sea bottom 

 is dredged the material is unconsolidated at all depths from 1 to 10 feet, and is 

 mostly an impalpable mud containing numerous shells quite loose in the 

 dredged material. (Verrill, op. cit., pp. 138 seqq.) 



2 Verrill, op. cit., p. 258, quoting a letter dated 1614, written by the 

 Eev. Lewis Hughes. "Here is also plenty of sea-foules, at one time of the 

 yeare, as about the middle of October, birds which we call Cahouse and 



