BY W. N. BENSON. 711 



The chief mineral-particles are large plagioclase-grains, with a 

 few quartzes, suggesting origin from a grano-dioritic rock. 



Where the Moonbi granite intrudes into these rocks, some inter- 

 esting contact-rocks are developed. They have been crushed, and 

 recrystallised into a fine mosaic of quartz and plagioclase, with 

 larger crystals of the latter mineral. The ferromagnesian portion 

 appears as green hornblende or actinolite. The foreign fragments 

 have suffered more or less alteration. Sometimes, when easily 

 affected, they appear only as minutely comminuted areas, or the 

 quartz-grains are crushed to single, small, clear mosaics. The 

 augite-crystals and grains pass into hornblende, and epidote or 

 clinozoisite is developed. The felspar-fragments generally seem to 

 suffer least, and occasionally they are enlarged. The fragments of 

 spilite are more or less sheared, and their original augite is 

 changed to actinolite. The most advanced stage, in the alteration 

 of these rocks, appears to be the development of long bands of 

 green hornblende, and biotite running irregularly parallel through 

 the finer-grained ground-mass. 



Specimens N.T., 460-465, exemplify this series of rocks, which 

 will repay more detailed study. 



The limestones of the Tamworth Series are of two kinds. The 

 radiolarian limestone, described by Messrs. David and Pittman, 

 and the purer, coralline limestone. The former, they say, is a dark 

 bluish-grey rock, weathering into a deep chocolate-brown, pul- 

 verent crust, with greenish patches. The greater part of the rock 

 is insoluble in hydrochloric acid ; no primary quartz is present. In 

 some examples, there are fragments of a chiastolite-bearing clay- 

 shale, and patches of chalcedonic quartz. The radiolarian tests 

 have their original substance preserved, in most cases, lie imbedded 

 in calcite, and are filled with the same material. Generally, the 

 tests are broken, the spines and outer tests suffering more than the 

 medullary tests. 



Near the Cuerindi homestead, on Hall's Creek (Manilla), a simi- 

 lar, brown, weathering-grey limestone occurs [M.B., 65]. It con- 

 sists very largely of tuffaceous material, such as fragments of 

 spilite, felspar-crystals, and grains of quartz. 



