BY W. N. BENSON. 491 



The object in the mind of the present author, when first com- 

 mencing work, was the purely petrological investigation of the 

 ultrabasic rocks; but, as the work progressed, a study of the 

 geology of the associated formations was found necessary in order 

 to determine the age of the intrusions ; and so many additional and 

 important problems presented themselves, that the work has 

 evolved into a general survey of the geological history of the whole 

 region. 



Considerable help has been derived from the earlier writings, 

 particularly in directing the attention to localities of interest. To 

 Mr. Donald Porter, of Tamworth, is due the suggestion that the 

 work should be commenced at Bowling Alley Point, which has 

 proved to be the "key" district; in many other points, also, his 

 intimate local knowledge has been most helpful. 



Except where otherwise stated, all the fossils have been deter- 

 mined by the New South Wales Government Palaeontologist, Mr. 

 W. S. Dun, to whom the author's best thanks are due. 



In the following pages, an account will be given of the general 

 geology of the Serpentine Belt, drawn from a study of about two 

 thousand square miles of country, involving six months' field work. 

 Half of this time was spent in the examination of the Bowling 

 Alley Point and Nundle area of about one hundred square miles. 

 Of this, a fairly detailed topographical and geological map was 

 prepared during a plane table-survey; the official two-inch land- 

 survey map being deficient in many details, in part of the area, 

 and totally lacking in the remainder. The contours are based on 

 aneroid observations. This will be given with Part ii. of this 

 work. 



The larger, northern portion was surveyed much more rapidly, 

 the official one-inch land-survey maps being sufficiently detailed. It 

 was impossible, in the time available, to obtain complete verifica- 

 tion of many of the points suggested, and further work will, doubt- 

 less, call for some modifications of the account here given, particu- 

 larly in the intricate area around Bingara; but nevertheless, it is 

 believed that the general description is in the main correct, and 

 may be admitted, at least, as a working hypothesis. 



