PEOCEEDINGS, APRIL. iii 



as reported, considerably above 170oz. of gold to the ton. Again, those 

 very solid pyrites contain no barytes, which latter minerals he first 

 discovered as the necessary adjunct to the gold. Supposing, however 

 as Mr. Johnston had stated, that the "Iron Blow is the result of 

 oxidation of pyrites similar to that now so largely associated with it," 

 it would be necessary to bear in mind that as proved from analysis they 

 had first to deal with a nearly non-auriferous bi sulphide of iron, con- 

 taining no baryta to speak of, and, secondly, that water is assumed 

 to have produced the rich pulverulent gold rock by means of the 

 decomposition of the former, and contemporaneously or subsequently 

 by means of infiltration filled the fissure, and that small disseminated 

 particles of baryta appeared either before or during the process of 

 oxidation. In his (Mr. Thureau's) opinion everything points to a more 

 drastic process of origination than simple and quiescent decomposition, 

 and to him it becomes clear to the close and careful observer of these 

 unique gold deposits in situ that dynamicil geology can alone account 

 for these strictly speaking volcanic products. Having had opportunities 

 for examining active " mad volcanoes " in the United States, and as the 

 process observable there in active progress assimilates a great deal 

 to what can be seen in its " dead state " at the " Iron Blow " of baryta 

 is substituted for silica, as matrix in the latter case, the question of 

 origin as to both metalliferous deposits is not only in his opinion, very 

 suggestive, but forms the only possible true solution of the case. 



In consequence of the absence of Messrs. Johnston and Ward it was 

 decided to postpone discussion until next meeting. 



TIDE OBSERVATIOlSrS AT HOBART. 



Mr. A. Mault read a paper on "Some tide observations taken at 

 Hobart during February and March, 1889," in which he stated that with 

 a wish, firstly, to obtain information connected with the drainage of 

 Hobart, and, secondly, to fix the mean sea level for geodetic and 

 engineering matters to get a series of tidal observations, he had arranged 

 with Captain Oldham, of H.M.S. Egeria, that observations be taken 

 at the New Wharf by the automatic tide gauge belonging to that boat, 

 and the result briefly was as follows : — 1. The tides are subject to a 

 large diurnal inequality, the highest high water being followed by the 

 lowest low water. The tide then rises to a lesser high water and falls 

 to a lesser low water. 2. With the moon's declination north the higher 

 high water follows the superior transit of the moon; with the moon's 

 declination south the higher high water succeeds the inferior transit. 3. 

 The greatest range of tide appears to occur about two days after the 

 moon has reached its greatest north or south declination : the least 

 range when the declination is zero. 4. H. V7.F. and C. occurs at 

 Hobart at 8h. 15m. Springs rise 3|ft. to 44ft. and 2ft., neaps 2|ft. In 

 the letter to him from Captain Oldham the following words occur : — 

 •' From these observations the mean tide level is 8ft. 2"7in. on the gauge 

 or 35'255ft. below the datum mark on the Town Hall." In the letter it 

 was also stated that, as these observations were only for one month 

 and as probably the mean tide level varies at different seasons, to get a 

 satisfactory result a year's observation should be obtained." He (Mr. 

 Mault) was glad to say that the Hobart Marine Board were obtaining 

 an automatic gauge, so that the observation could be continued. For 

 the purpose of more readily comprehending the information contained in 

 those observations, he had prepared diagrams showing the occurrence of 

 springs at greatest declination, and oot at new and full moon, and that 

 there is no "age of the tide" at Hobart. Diagrams were also 

 appended, showing, for comparison, a fortnight's tide curves at Hobart, 

 and a fortnight's at Bombay, and another representing a normal curve of 

 lunitidal intervals. The irregularities which appeared by these 



