GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 447 



named Prospect Hill — rising about 200 feet above the level 

 of the surrounding country, and flanked on the west by the 

 Prospect Reservoir, which conserves the water supply of 

 Sydney. The hill covers an area of about 700 acres, and 

 is situated immediately to the south of the main Western 

 Road, some 18 miles from Sydney. It is accessible from 

 Toongabbie station on the Main Western Railway, which 

 lies nearly three miles to the north. The geological sketch 

 map of the country in the vicinity of Sydney, published by 

 the Mines Department of New South Wales, indicates the 

 situation of the mass, and its relation to the neighbouring 

 dykes and necks which are composed of similar basic rocks. 



2. Bibliography. 



Owing to the position of Prospect Hill on the once much 

 travelled main western road, we find references to it, and 

 brief accounts of its geology, very early in the history of 

 the State. Since the large quarries were opened, Prospect 

 has been a favourite haunt of geologists, yet no systematic 

 description of the whole mass of the eruptive rock has been 

 attempted hitherto. The following is a list of the more 

 important works containing notices or brief descriptions of 

 the igneous mass at Prospect : — 



P. Lesson — Voyage autour du monde, Paris, 1826 ; vol. i, 

 p. 328. 

 M. Lesson made a journey to the Blue Mountains, and 

 remarked " . . ce fait curieux d'une colline elevee, entiere- 

 ment de dolerite, dont le pied est enveloppe de gres." 



J. D. Dana — Report of United States Exploring Expedition 

 of 1840. 



In 1840 Dana spent some months in New South Wales, 

 and made some very interesting investigations into its 

 geology. The results of his work are embodied in the very 

 rare volume giving an account of the above expedition. 



