September 1, 1894.] 



KNOWLEDGE. 



201 



valid. AVhatever the cause, disturbances of greater energy, 

 and on a vastly greater scale than anything we witness 

 here, are manifestly in continual operation. 



One other point should be noted. The forward motion 

 of the group was considerably greater than the longitudes 

 given above would indicate, for they were computed with 

 an assumed rotation period of '25'38 days ; but this period 

 corresponds, according to CarrLngton's law, to a latitude 

 of 15°. For spots in north latitude 25°, the daily angular 

 rotation should be 831' instead of 851', and the group on 

 October 10th should have been some 27° behind its place on 

 July 10th, instead of not quite one-tenth of that distance. 

 The movements of the group in a forward direction were 

 therefore one hundred miles an hour swifter, as compared 

 with the photosphere in that latitude, than the foregoing 

 figures would indicate. 



It may also be pointed out, as showing how difficult it 

 is to obtain a satisfactory determination of the solar rota- 

 tion from the suuspots, that the group in question would 

 give a different value for the rotation period from each of 

 its four apparitions and from each of the three periods 

 during which it is in the further hemisphere. And that, 

 further, we should get different periods from the group as 

 a whole, and from the stable and well-defined leader spot, 

 which always constituted its principal member. Two of 

 these values, as given by the leader spot, would correspond 

 closely to the theoretical rotation for the latitude ; the 

 others would all be much shorter, as this table shows : — 



Limiting Dates. 



July 11-July 20 

 July 20-August 4 

 August 4-August 16 

 August IG-September 1 

 September 1-September 13 

 September 13-September 28 

 September 28-October 10 



This question of the rotation period for different latitudes 

 renders it a difficult matter to trace with certainty an 

 interrupted disturbance. Yet it is not uncommon, when 

 the site of some great outbreak is traced back for two or 

 three rotations, to find that it has for a long time past 

 been the seat of short-lived displays. Thus, the chief 

 group of 1891, No. 2293, had its centre in longitude 221-5 

 and north latitude 21-8" during its greatest development, 

 August 29th to September 10th. The following table will 

 show how, for several months before, outbreaks of varying 

 importance and duration had been common in the same 

 locaUty : — 



No. of (rroup. Limiting Dates. 



2298 August 29-September 10 



2272 August 1-10 

 2254 July 6-17 



2240 June 17-20 



2235 June 10-20 



2222 May 22-25 

 2218 May 16 



2203 April 19-25 



Similarly, after the dissolution of the group a number of 

 short-lived groups were scattered over the entire region 

 which it had occupied. 

 No. of Group. Limiting Dates. 



2306 September 24-October 5 



2828 October 22-November 2 



2329 October 23-30 



2330 October 24-27 

 2835 October 28-November 2 



Here, again, the final position for the centre of disturb- 

 ance is nearly the same as the original position, in spite 

 of the high latitude. The real fountain of the formation 

 of the spot, therefore, would appear to have rotated with 

 a speed which was independent of latitude, and which did 

 not greatly differ from the mean period of the spots. 



ON THE ORIGIN OF THE GOLD IN 

 QUARTZ VEINS. 



By Henry Louis, Assoc. B.S.M., F.I.C., F.G.S., 

 Mem. Amer. Inst. Min. Eng., etc. etc. 



WHENEVER we find rival sets of theories held 

 by acknowledged authorities in any branch of 

 science, one of the best services that can be 

 rendered to that science is the collation and 

 criticism of these theories as applied to some 

 one closely defined subject. In no other way can the 

 weakness and strength of the respective positions be as 

 clearly seen, and the probabilities in favour of each as 

 successfully studied. 



The general question whence the various substances 

 have come that constitute the filling of mineral veins is 

 still to-day, in spite of the immense amount of work that 

 has been bestowed upon it, one of the most debatable 

 within the whole range of geology. Whilst no one nowadays 

 doubts that the filling up of the fissures, which constitute 

 veins, has been brought about by aqueous or hydro-thermal 

 agencies, and that the various minerals have been introduced 

 in solution, opinions vary greatly as to the direction whence 

 these mineral solutions have come : they may have entered 

 the open fissure from above or from below, or may have 

 been forced in by pressure or by capillary attraction through 

 the pores of the rocks that form the walls of the fissure. 

 There are accordingly three main schools of theorists — 

 the descensionists, the ascensiouists, and the lateral secre- 

 tionists. Prof. Lobley has ably sketched the theory of 

 the origin of gold in quartz veins from the descensionists' 

 point of view, and it should prove a profitable and an 

 mteresting task to now attack the same problem from the 

 opposite standpoint, and to briefly summarize what may 

 be considered the case for the opposition. 



It is hardly worth while to insist upon the primary 

 point that gold, like other minerals, has been deposited 

 from solution. Prof. Lobley has accumulated a con- 

 siderable body of negative evidence on this head, his proofs 

 resting upon the fact that gold does not exist within regions 

 of known volcanic action. This evidence is hardly, 

 however, as satisfactory as it might be ; first of all because 

 it is negative, and secondly because there are at any rate 

 two well-known and oft-quoted localities — Sulphur Bank, 

 California, and Steamboat Springs, Nevada — where gold 

 may actually be traced in process of deposition, both of 

 which offer unmistakable evidence of volcanic phenomena 

 in the shape of hot mineral waters and gases. According 

 to some authorities, too, the famous Mount Morgan Mine 

 in Queensland is simply a geyser deposit, though it is but 

 right to say that this theory has by no means passed 

 unchallenged. I recently attempted to obtain some more 

 direct proof of the aqueous origin of vein gold, and for this 

 purpose compiled as complete a list as possible of all 

 minerals known to accompany gold in auriferous veins. 

 (" The Mode of Occurrence of Gold," Minendopical 

 Maiiazine, Vol. X., No. 47, p. 241.) This list comprised 

 no less than seventy-seven mineral species ; fully two- 

 thirds of these, however, are beyond doubt decomposition 

 products of others, which had as clearly been the minerals 



