1901. ENTOM( 'LOGICAL SOCIErY. 39 



2. Siphoiiida. 



(a) Integro-Palluilia. 



(b) Siuu-Pallialia. 



The animals of the tirst section are without the respiratory tubes possessed 1 y the Sipho- 

 iiida, and it is with this first section that we have to do. 



The first group, Pleuroconcha, rest in their natural position with one valve beloiv and the 

 uther above. They have but one large muscular impression in the centre of each valve, which 

 forms a shallow pit, occu])ied by the muscle which keeps the Vcilves closed. • An example is the 

 oyster and Ambonychia radiata of the Hudson River Group, Lower Silurian. 



The second group, or Orthoconcha, are without siphonal tubes, but their valves are ri<i]tt 

 and left, instead of upper and under, as regards its normal position, and the muscular impres- 

 sions are two in each valve. The most remarkable of this genus is the Megalomus Canadensis, 

 of Hall, which occurs in great numbers in the Guelph formation, principally in the form of 

 niternal casts, very few specimens showing the original shell. 



The Meg. compyessus of Nicholson, is allied to the M. Canadensis. It is smaller and more 

 compressed ; the umbones are more prominent, and the pallial line more distinct. Other fossils 

 include many varieties of the Murchisonia, and these examples on the table are M. Loganii. 



All these specimens are, however, internal casts only, very few having been found present- 

 ing the outer shells, and in the case of Megalomus, scarcely anything is known of its outward 

 appearance. The filtration of water and the jireseuee of carbonic acid in the dolomite have 

 destroyed the organic matter of the shell, and left the cast of the interior. There is a great 

 quantity of water in these rocl^s, saturating the stone heavily in the lower portions, which, 

 when freshly quairied, is quite soft, becoming very hard on losing a portion of the water on 

 contact with the atmosphere. Some of the quarries contain few fossils, others are full of them, 

 and while one quarry may produce good specitnens, the majority from others are of scarcely 

 any use for cabinet purposes. Some fossils are also found in the gravels, but are very badly 



worn. 



j. l. goodburne. 



Methods of Concentrating Gold. 



There are two methods of concentrating gold — by means purely mechanical and by chemicals. 

 For the efficient separation by the former process innumerable appliances have been invented 

 whose fundamental principle is in nearly every case based on the great specific gravity of gold. 



For separating low grade gold ores an interesting appliance has recently come into general 

 use in Western America. It consists of an endless rough-flanged Vjelt passing over two pulleys, 

 ' me slightly lower than the other, thus giving the upper surface of the belt. JSTear the lower 

 wheel the pulverized ore is deposited and is carried upward by the revolving belt which meets 

 'I stream of cold water. This carries off the quartz, leaving the gold adhering to the rough belt 

 whence it is later deposited in settlers. 



Cyaniding and Chlorination have of late received much attention from mining men. The 

 former particularly is made use of in a great majority of up-to-date mills. 



The ore is crushed to a pulp before cyaniding and thrown into cyanide vats, after which a 

 solution of cj'anide of potassium is added to dissolve the finer particles of gold. The solution is 

 drained oft' into " zinc " tanks filled with zinc clippings, where the zinc displaces the gold and 

 the metal is deposited with the zinc slimes whence it is easily recovered by retorting. 



In chlorination it is not necessary to crush the ore so fine. It is also roasted before being 



passed to chloriaation vats to break up all sulphides. After the barrel is charged with the 



reciuired amount of cliloride of lime and sulphuric acid it is revolved slowly from three to eight 



'hours, when the gold solution is drawn off through a filter into lead-lined settling tanks. From 



this the gold may be obtained by SOo H^,S or by the charcoal method. 



