464 



NATURE 



[March 20, 1890 



wood has found Pelonaia in some numbers in the intestine of 

 the common dab. 



Amongst anemones, A. meiembryanthemum is certainly a 

 favourite food of the cod, and is not uncommon on the carapace 

 of Cancer pagurns. It is difficult to see in what way the ane- 

 mone is there protective to the crab. Both young crabs and 

 anemones (of this and some other species) are equally preyed 

 on by the cod ; and though the crab may perhaps be big enough 

 (as in a recent specimen 5 inches broad) to enjoy immunity from 

 the cod's attack, yet, by parading such a gaudy bait, it must at 

 least run the risk of a severe shaking. It may be added that, 

 in the last-named case, the anemone quitted the crab, when 

 moribund, for a more desirable basis. 



Ernest W. L. Holt. 



St. Andrews Marine Laboratory, N.B., March 9. 



Abnormal Shoots of Ivy. 



The accompanying sketch represents a condition which is ex- 

 hibited by a certain group of ivy plants in the neighbourhood of 

 Plymouth. The plants are rooted upon the top of a high bank, 

 which bounds the southern side of the road from Mount Edg- 

 cumbe to Tregantle ; the branches pass downwards from the top 

 of the bank on to its northern side. 



The young shoots of each plant are conspicuous, because 

 their leaves appear red, and so contrast strongly with the green 

 of the older leaves. This appearance is due to the fact that the 

 lower surface of each leaf is uppermost. 



The sketch represents the terminal portion of a young shoot. 

 The growing point is directed downwards. The three terminal 

 leaves, a,b,c, have their upper surfaces directed upwards. The 



J \-i 



leaves beyond these, however (d,e, Ac), are twisted in a two- 

 fold way. First, each leaf-stalk is twisted on its own axis, so 

 that the lower side of the leaf is directed upwards ; and 

 secondly, the apex of each leaf is rotated through 180°, so that it 

 points away from the growing point of the shoot which bears it, 

 towards the root. 



This twisted condition is exhibited by about twelve or fourteen 

 leaves on every young shoot — say, through a dozen inches from 

 the growing point. The older leaves lose both kinds of torsion, 

 so that each old leaf has its upper side uppermost, and its apex 

 is directed towards the growing point of the stem. The under 

 sides of the older leaves have completely lost their red colour. 



The condition described is exhibited by all the shoots of a 

 plexus of ivy plants just beyond the fifth milestone from Mount 

 Edgcumbe, on the road above mentioned. It is absent in all 

 the many bushes and creeping masses of ivy which grow on the 



same bank of the road between this point and Mount Edgcumbe. 

 Whether all the plants composing the abnormal plexus are the- 

 offspring of a single parent cannot now be determined. 



Plymouth, March 10. W. F. R. Weldon. 



Earth-Currents and the Occurrence of Gold. 



Gold has been so large a factor in the prosperity and great- 

 ness of Australia, that the interesting subject of the origin of gold 

 drifts and reefs must always possess to us something more than 

 a purely scientific attraction. In the earlier days of the gold- 

 fields there was among the diggers much speculation, of a 

 scientific and semi-scientific nature, as to the processes by which 

 Nature had produced the accumulations of coarse and fine gold 

 dust which it was their business to extract from the alluvial drifts. 

 The most obvious explanation, of course, was that the grains of 

 gold had an origin similar to that of the debris and detritus of 

 various characters which made up the alluvium itself ; and this 

 explanation seemed to harmonize so completely with the general 

 processes of Nature that at one time it was almost universally 

 accepted as the correct one. But many thoughtful mining 

 authorities had their doubts upon the subject, and these doubts 

 were not founded, as so frequently happens, upon mere prejudice, 

 but were fortified by the fact that certain phenomena character- 

 istic of the occurrence of drift gold were not only not explained 

 by the " detrital hypothesis," as it is called, but were absolutely 

 inconsistent with it. Chief among these objections may be 

 mentioned the undoubted generalization that drift gold is nearly 

 always purer than the gold in the reefs of the neighbourhood 

 in which it occurs. No explanation as to the long distances to 

 which grains of gold might be conveyed, or to the possible 

 purifying effects of natural chemical action, made up any satis- 

 factory explanation of the known facts, and accordingly under 

 the detrital theory these facts had to remain shrouded in mystery. 

 Then, again, it was a frequent occurrence for gold to be found so 

 peculiarly embedded in pieces of wood, or in conjunction with 

 natural crystals of minerals, such as the sulphides, that those who 

 were constantly being brought into contact with such phenomena 

 were firmly convinced that at all events there was a certain pro- 

 portion of the gold found in alluvial drifts which had its origin 

 in some other source than the breaking down of quartz reefs by 

 the ordinary processes of Nature. The majority of those who 

 held to this belief had at first but little scientific knowledge of 

 natural reactions ; and when questioned as to their theory on the 

 subject, they were accustomed to say of the alluvial drift-gold, 

 that it appeared to be actually growing — a statement which 

 sometimes provoked, not unnaturally, a smile of pity for mis- 

 placed credulity. 



These objectors, however, were right. Of this there is now 

 scarcely the shadow of a doubt. It would be tedious to trace 

 the steps by which such a strange conclusion has come to be 

 virtually established. Suffice it to say that at the present day 

 there are but few scientific men in Australia who have studied 

 the subject who do not hold that by some agency or another the 

 gold that is in our alluvial drifts has been formed, and probably 

 is at present accumulating at the present moment, in its present 

 position. It seems probable, indeed, that drift gold has its 

 origin in the salts held in solution by the water by which it was 

 formerly supposed to have been merely carried from one place 

 to another. The most common salt of the precious metal is 

 chloride of gold ; and of this salt there is an appreciable quantity 

 present in sea water along with the common sea salt, which, of 

 course, is mainly chloride of sodium. In geological epochs, when 

 the rocks of our present gold-fields were submerged below the 

 ocean, and later on, when they held upon their surfaces vast im- 

 prisoned lakes of salt water, it is probable that they became 

 saturated with sea water and retained large amounts of gold in 

 solution. According to a computation quoted by Mr. Skey, the 

 Government Geological Analyst for New Zealand, it is probable 

 that every cubic mile of rock contains something like a million 

 ounces of gold. Hence the underground streams of Australia, 

 in certain districts, are particularly rich in salts of the precious 

 metal, and there is an enormous area over which slight quantities 

 of gold can always be obtained, while surface streams which are 

 fed by deep-seated springs accumulate gold upon alluvial flats 

 and hollows. Some of the gold found in such streams may 

 undoubtedly be ascribed to the destruction of quartz reefs. It 

 stands to reason that these reefs, like other rocks, must contri- 

 bute to the debris in the beds of rivers and streams. But most of 

 the purer alluvial coarse gold has evidently a different origin. 



