510 GREAT SERPENTINE BELT OF NEW SOUTH WALES, i., 



liminary note (15), the writer termed this a diabase, and considered 

 it of later date than the serpentine. The term, however, has been 

 altered, in accordance with modern British nomenclature. The 

 consideration of the age is a different matter. The field-relations 

 in the Nundle region were insufficient to determine, with precision, 

 the position and origin of the rock, and the petrological peculiarity 

 had not been noted. It was thought best to consider it as a later 

 differentiate of the same magma as the serpentine, and, therefore, 

 to be looked for in connection with that rock. At the same time, 

 it did not escape notice, that the dolerite-intrusions ran roughly 

 parallel to the strike, and were confined to the Tamworth (there 

 called Bowling Alley) series of rocks. The later work in the 

 northern district, and the detailed petrology have added much in- 

 formation. Several other distinctive types of dolerite have been 

 found, but that which is analogous to the Nundle dolerite, occurs 

 in rocks of the Tamworth Series only, whether these lie east or 

 west of the serpentine-belt. Where the Tamworth rocks are not 

 developed, the serpentine is quite unaccompanied by dolerites of 

 this character. Moreover, the so-called andesitic lavas in the Tam- 

 worth Series, asssociated with the dolerites, prove to be spilites. 

 There are many occurrences cited by Steinmann(16), and Messrs. 

 Dewey and Flett(l7), of Ordovician Hercynian, and Alpine erup- 

 tion-periods, where sediments, usually radiolarian, are associated 

 with tuffs, spilite-flows, and intrusive sills of dolerite; and it 

 seems most probable, in view of the later observations, that a like 

 association holds for the rocks under consideration here. In all, 

 these sills are about 2,500 feet thick in the Bowling Alley Point 

 district, but are extremely irregular. The present group of 

 dolerites are then connected with the spilites, not directly with the 

 peridotites ; and as, in the north, the dolerites have undergone the 

 crushing, in areas east of the serpentine-line, they may fairly be 

 considered to be of earlier date than the serpentine. These dolerite- 

 intrusions were probably almost contemporaneous with the spilite 

 lava-flows, possibly somewhat later. 



After the succeeding explosive action that produced the Baldwin 

 Agglomerates, there was a long period of quiet. Then igneous 



