ON THE ROCKS OF THE IIAURAKI GOLD-FIELDS. 245 



the stony desert at long distances apart, the sand has been 

 derived from an undergronnd source through the pressure of 

 subterranean water. There was, in all probability, an outlet at 

 one time connecting the Mesozoic basin which occujjies the centre 

 of Australia with the ocean. If we suppose a sudden or gradual 

 closing up of this outlet to have taken place through the subsidence 

 of the land or any other cause, the water not having any vent to 

 escape by, would accumulate in the porous strata until under 

 sufficient pressure to force its way to the sui-face along cracks or 

 through holes caused by such pressure, and bring with it the 

 sand, in a similar manner to the present mud and sand springs, 

 and thus have caused the depressions now occupied by the great 

 lakes such as Lake Eyre, which is below the level of the sea. 



G.— THE DESERT SANDSTONE OF AUSTRALI 

 By the Rev. J. E. Tenisox Woods, F.G.S, F 



Friday, August 31. 

 The following papers were read : — 

 l._ON THE ROCKS OF THE HAURAKI GOLD-F 



By F. W. HuTTON, F.G.S., Professor of Biology, Canterbury 

 College, Christchurch, New Zealand. 



The Hauraki Gold-mining District, Auckland, New Zealand 

 extends from Cape Colville on the north to Te Aroha on the south 

 a distance of about one hundred miles, and includes the sub 

 districts of Coromandel, Tapu, Thames, Ohinemuii, and Te Aroha. 

 In geological structure it consists of a sedimentary formation of 

 slates and sandstones, not younger'than Triassic, overlain quite 

 uncomformably by a younger formation, chiefly of volcanic origin, 

 which is not older than Cretaceous, and in which all the gold 

 mines are situated. To this statement all geologists are now 

 agreed, but opinions differ as to whether any long interval of time 

 separates the volcanic rocks into two distinct seines, the older of 

 which is alone auriferous, or whether all should be considered as 

 parts of one. This point will not be decided until the countiy in 

 the neighbourhood of Cabbage Bay is satisfactorily made out. In 

 this district the limestones of Oligocene age containing Uemipatagim 

 tiibercidatus, Pentacrinus stellatus, Osfrea Wullerstorfii (?), as well 

 as Fusus, Turritella, Cucullcea, and other genera are found in 

 close proximity to the auriferous volcanic series ; but the 



