360 Watts and Newton — Hocks from Solomon Islands. 



"These five specimens are hard limestones varying from fine, 

 close-grained to coarsely cavemons rock. The first specimen from 

 Florida Island (F. 278) has the finest, and the third (F. 279), the 

 coarsest texture of the three. Under the microscope they are Been 

 to be composed of similar materials, namely, fragments of nullipores, 

 corals, and foraminifera, the last-named being chief!}' in the finer 

 material filling in the larger cavities. In the first (F. 282) of the other 

 specimens the rock is much coarser and more cavernous than in the 

 three above noticed, and some of the surfaces are covered by a 

 calcareous coating (stalagmite?). Under the microscope, pieces of 

 molluscan shells, corals, and possibly spines of echinoderms, were 

 detected, as well as large foraminifera (Amphistegina, etc.). This 

 rock closely resembles Dr. Guppy's figure. 1 The last of these coral 

 rocks (F. 290) was found six feet above high-water mark. It is 

 the coarsest rock of the series, and is chiefly formed of nullipores 

 and corals, the cavities being filled in with debris, in which are 

 foraminifera and other small organisms ; few or no sponge spicules 

 were detected in any of these fine coral rocks." 



B (/i) Under the name of chalky coral rock, Dr. Guppy describes 

 a set of limestones which " in the general composition resemble the 

 rocks of the second group of coral limestones [B (/)], but differ con- 

 spicuously in their chalk-like appearance and in being more friable." 

 Microscopic examination of one of Dr. Guppy's specimens from the 

 Shortland Islands bearing this designation (F. 299), does not accord 

 exactly with this general description. The rock shows that minute 

 crystals of dolomite are of frequent occurrence, and a chemical test 

 reveals a small proportion of magnesia. This fact has already been 

 made known by Dr. Guppy in a rock which corresponds closely with 

 the following description. 2 Of this rock Mr. Newton remarks as 

 follows : — " Under the microscope, nullipores are very distinct, and 

 there is evidence that other organisms have been present, such 

 probably as would make up an ordinary ' mixed coral rock,' but these 

 are so decomposed as to leave mere traces of their original shape. 

 It is worthy of remark that the nullipores seem to be able to resist 

 the action which has caused the alteration of this rock better than 

 any of the animal organisms, and perhaps this may be due to the 

 different state of the carbonate of lime of which they are composed." 



Specimens from the south coast of Mbulo Island (F. 297) and 

 from the southern coast of New Georgia, on the other hand, appear 

 to correspond with Guppy's general description. They are friable, 

 white, chalky limestones, containing abundant relics of organisms, 

 which are mostly in a fragmentary condition. They are set in a fine 

 calcareous mud, in which I have seen no evidence of dolomite. Mr. 

 Newton adds that the slide contains " pieces of corals, nullipores, 

 foraminifera, molluscan shells, etc., and is, in fact, one of the ' mixed 

 coral rocks ' in a somewhat friable condition." 



We now proceed to describe a few types of rocks not included in 

 Dr. Guppy's classification. 



1 Trans. Roy. Soc. Eclin., vol. xxxii (1887), pi. cxlv, fig. 3. 



2 " The Solomon Islands, then- Geology," etc., p. 74. 



