

92 



„„,ni«?:™!j; 



GEOLOGICAL RESEARCHES IN 



Fig- 13 



,,m..ttiliUiiilli(Sil>iffiS»iiiSii«iS^^ 



a. Reservoir, h. Sluice-ditch, c. Rubble of the drift, d. Aurif. drift, e. Creek. /. Bedrock, g. Mats. 



At the place where I saw this process, the surface of the bed rock, in this case 

 the marine terrace deposit, was sufficiently high above the creek to give a rapid fall 

 in the sluice-ditch. 



The bed of a rivulet is chosen for the Avork. A reservoir (a) is dug and 

 dammed, and the bed of the rivulet (6) cleaned out and made regular. This done, 

 the banks (cZ) are broken down into the stream where the force of the current con- 

 centrates the gravel, carrying off the sand and clay. The workmen then place 

 themselves in pairs up and down the stream near and below the broken-down bank. 

 Each man is provided with a coarse mat, about two feet long by one foot broad, 

 which he places lengthwise in the stream, keeping it down with one foot on the 

 lower end, at the same time partially stemming the current. He then hoes the 

 gravel on to the mat, much of the old gravel going off below as fresh arrives from 

 up stream. 



At intervals the mat is carefully removed and washed out into a very shallow tray 

 or batea (Fig. 15), aboard about eighteen inches long by a foot broad, hollowed out, 

 and having a circular depression near one end for the concentrated head. Of the 



black sand obtained on this board, the head contain- 

 Fig. 15 ing the gold is saved. 



In this manner the gravel is pretty well exhausted 

 of its gold, very little being obtained 'by the men 

 farthest down the stream. The Avorking progresses 

 sideways, into the banks, and up stream, the current 

 being kept near the banks as these recede from the 

 centre of the stream. As the space between the 

 banks Avidens, the coarser material that resists the 

 force of the Avater is throAvn up into a pile of loose 

 masonry (c) Avhich increases in length and breadth as the Avork advances. 



