﻿THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE II. VOL. IV. 



No. XII.— DECEMBER, 1877. 



L — On the Oocubkence of Chalk in the New Britain Group. 



By Professor Liversidge, Etc., Etc., 



University of Sydney. 



(Read before the Eoyal Society of New South Wales, July 4, 1877.) 



IN the following brief notice it is my wish to communicate to the 

 Society a description of the physical properties and chemical 

 composition of one of the geological specimens recently brought 

 from the above group of islands. 



The specimen which I now have the honour to lay before you is 

 not only interesting in itself, as an example of what is known as an 

 organically formed rock, since it is built up almost entirely of the 

 calcareous skeletal remains of organic forms ; but it is interesting 

 in a still higher degree, as it apparently indicates that a most impor- 

 tant geological discovery has been made of the presence of chalk in 

 a hitherto unknown, and even unsuspected, locality. 



In October last, the Rev. G. Brown, Wesleyan missionary, 

 brought amongst other specimens from New Britain and New Ire- 

 land (New Britain Group, latitude 4° S., and 150° E. longitude) 

 certain grotesque figures of men and animals, which had been 

 carved by the natives of the above islands out of a soft white some- 

 what pulverulent material, having much the appearance of plaster 

 of paris or chalk. Some of these figures were deposited in the 

 Museum, and a fragment broken off from one of them was placed in 

 my hands for identification. 



On examination the remains of numerous Foraminifera are at once 

 detected, the forms of the larger ones being plainly visible, even to 

 the unaided eye ; under the microscope the whole mass of the rock 

 is seen to be almost entirely composed of the shells and fragments 

 of shells of Foraminifera, the remains of GlohigerincB being most 

 abundant. To obtain the shells of the Foraminifera free from the 

 cementing calcareous matter, it is only necessary to gently rub the 

 surface of the specimen with a soft tooth or nail brush under a stream 

 of water, when the whole surface of the fragment submitted to the 

 operation speedily becomes studded with the minute shells and frag- 

 ments of shells of Foraminifera, now left standing out in relief. To 

 free the Foraminifera perfectly from the accompanying powder, it is 

 sufficient to dry the collected debris and to place it upon the surface 

 of some clean water contained in a glass beaker or other vessel; the 

 larger or more cavernous Foraminifera float on the surface of the water, 

 while the broken fragments, much of the amorphous powder, and many 

 of the denser Foraminifera, are deposited at the bottom of the vessel 

 as a sediment. The very light and finely divided parts are got rid of 

 by decanting the milky supernatant liquid. In the sediment the 



DECADE II. — VOL. IV. — NO. XII. 3i 



