542 



NA TURE 



[Oct. 4, 1888 



the final " exhaustive explosions of abnormal violence," 

 together with the vast sea and air waves, and the 

 subsequent optical phenomena, which accompanied that 

 of KrakataT). 



Prof. Judd next deals with the nature of the materials 

 ejected, and draws attention to the different physical cha- 

 racters presented by the lavas ejected from Krakatab at 

 different epochs, the final compact lavas of 1883 being por- 

 phyritic pitchstone, and obsidian, containing about 70 per 

 cent, of silica, and so nearly identical chemically with those 

 of some of the earlier outpourings as to suggest refusion. 



The heavier lava dust which fell in Java and was 

 examined by numerous geologists, including Prqf. Judd 

 himself, exhibits a peculiarity which he considers to be 

 without precedent, in that it contains almost every variety 

 of feldspar crystals. The base in which these crystals was 

 found to be embedded presents great differences in its 

 fusibility, the pitchstone melting with great difficulty, and 

 the obsidian with ease. This latter point, in combination 

 with other circumstances, leads Prof. Judd to one of the 

 most important of his conclusions, viz. as to how 

 eruptions come to differ not merely in magnitude but in 

 quality : for example, how a volcano such as Krakatab at 

 one time emits massive and viscous lava-streams as it did 

 in former times ; at another, pours forth a more liquid 

 lava ; and again, as on this occasion, bursts out with 

 explosive violence into an eruption in which most of the 

 lava is converted into pumice. He considers that the 

 older lavas have been chonically acted on by water which 

 has slowly percolated through the crust in the vicinity, 

 and that the new compounds thus produced are not only 

 more readily fusible, but more easily convertible into 

 pumice. Volcanic action is thus concluded to be brought 

 about not directly by the physical action of externally 

 derived water, but by changes in the physical properties of 

 rocks chemically altered through the medium of such water. 

 In connection with the optical effects which were 

 witnessed subsequent to the eruption, and which are found 

 to be connected chiefly with the finer solid ejecta, Prof. 

 Judd finds evidence, both from a study of the Krakatab 

 pumice as well as the finer dust which fell at great 

 distances, that by the unusual violence of the explosions 

 during the major outburst a large quantity of the very 

 finest threads and dust of volcanic glass was thrown out 

 into the higher atmospheric regions, where it might re- 

 main suspended for very long periods. He also points 

 out that the absence of any sign of materials characteristic 

 of Krakatab in the rainfall of distant places is no evidence 

 against their wide diffusion, since the most characteristic 

 substance in the Krakatab dusts was rhombic pyroxene, 

 and this by reason of "its high specific gravity and its 

 slight friability would be among the first to fall." 



Prof. Judd brings his section to a close by a general 

 review of the circumstances which have led him to adopt 

 the view already enunciated regarding the cause of 

 volcanic action, viz. that the liquidity of a lava and the 

 violence of an eruption depend on the extent to which the 

 lava has, as it were, been hydrated under the influence of 

 slow aqueous percolation. Lavas of precisely the same 

 composition, and at the same temperature may vary 

 greatly in their eruptive action simply by the changes 

 thus effected in their fusion-points. This refined form of 

 the volcanic theory, which is put forward by Prof. Judd, 

 appears to show that the Vesuvian stage of eruption is a 

 paroxysmal form of earth sickness, due to lava gases in- 

 directly generated by water action, while the quiet out- 

 pourings both from cones and fissures which have taken 

 place so widely both in the past and present ages, repre- 

 sent the more normal welling up of lava which has been 

 less altered by water action. For this reasonable 

 deduction and the clearer insight afforded into the 

 modus operandi of volcanic and seismic phenomena, 

 we are, without doubt, indebted to Krakatab. 

 ( To be continued.) 



THE BRITISH ASSOCIATION. 



SECTION H. 1 



anthropology. 



Opening Address by Lieutenant-General Pitt-Rivers, 

 D.C.L., F.R.S., F.G.S., F.S.A., President of the 

 Section. 



II. 



The accompanying map of Great Britain shows the monu- 

 ments that I have been the means of obtaining by the consent 

 of their owners. 



The Pictish Tower at Mousa in the Shetlands, which is well 

 known to be the best preserved monument of this class in the 

 country, has been included by the owner, Mr. Bruce, and some 

 necessary repairs have been done to it by the Government. In 

 the Orkneys the owners of the scheduled monuments declined to 

 make use of the Act, but they are well looked after. The same 

 applies to the Bass of Inverurie, the Vitrified Fort on the hill of 

 Noath, the Pillar Stones at Newton, in the Garioch, and the 

 British settlement at Harefaulds, in Lauderdale, which latter, 

 however, is in such ruinous condition that the remains 

 of it are scarcely worth preserving. The Suenos Stone 

 near Forres ; the Cairns at Clava, on the banks of 

 the Nairn ; the Cat-stane at Kirkliston; the Burgh of Click- 

 anim, have also been withheld by their owners, but most of 

 them are very well taken care of. The Cairns at Minnigaff were 

 nearly destroyed before they were scheduled, and are not worth 

 preserving. The inscribed stone in St. Vigean's churchyard is 

 preserved in the pdrch of the church, but it is not included. On 

 the other hand, Edin's Hall, the largest and most southern of 

 the remains of the Pictish Towers in Berwickshire, has been 

 included by Mr. J. S. Fraser-Tytler ; the Black and White 

 Catherthuns have been added by Miss Carnegy Arbuthnot ; 

 both these are large camps having ramparts of stones and earth- 

 works round them, and they are described in General Roy's 

 work. The Pictish Towers at Glenelg have been included by 

 Mr. James Bruce Bailey ; they are in a very bad state of repair, 

 and have been propped up by the Government. The inscribed 

 stones at Laggangairn, New Luce, have been included by Lord 

 Stair ; they are at a great distance from any road or habitation, 

 and the protection afforded them, beyond the powers contained 

 in the Act, must be regarded as nominal. The Peter's stone, 

 on the road from Wigton to Whithorn, has not been added ; it 

 is an important stone, and is in a dangerous position ; it has 

 already suffered damage, and it is to be hoped it will be included 

 hereafter. The chapel on the Isle of W T hithorn, supposed to be 

 that built by St. Ninian, has been included by Mr. R. Johnstone 

 Stewart ; this was not in the schedule. The Pillars of Kirk- 

 madrine have been included by Mrs. Ommaney McTaggart ; 

 they are the earliest Christian monuments in the country. I 

 suggested that Government should contribute towards building 

 a small chapel to contain them, which has been done. The 

 Cross at Ruthwell, with its remarkable runes, which were 

 gradually being destroyed and covered with lichen, so that its 

 inscription could not be read, has also been added. I suggested 

 that the Government could contribute towards building an annex 

 to the neighbouring church to contain it, which has been done. 

 This was not in the schedule. The cup-marked rock of 

 Drumtrodden, Wigtonshire, has been added by Sir Herbert 

 Maxwell, and Government has granted a certain sum towards 

 building a shed over it to preserve it. It was not in the 

 schedule, but is a good example of its class. Barsalloch 

 Fort, Wigtonshire, the Moat Hill of Druchtag, the Drumtrodden 

 standing stones, Wigtonshire, have also been added by Sir 

 Herbert Maxwell. St. Ninian's Cave, with its early Christian 

 crosses, has been included by Mr. Johnstone Stewart. In the 

 Island of Lewis the remarkable standing stones in the form of a 

 cross at Callernish, and the Broch at Carloway, have been 

 added by Lady Matheson. This latter is, next to Mousa, the 

 best Pictish tower in the country. In Cumberland, the Stone 

 Circle on Castle Rigg has been put under the Act by Miss 

 Edmondson. In Westmoreland, Arthur's Round Table, an 

 earthen circle with a ditch in the interior, and Mayborough, a 

 large circle with an embankment of stones and the remains of a 

 stone circle within, has been included by Lord Brougham. In 

 Derbyshire, Arborlow, a large circle similar to Arthur's Round 

 Table, with the remains of a stone circle, the stones of which 

 are prostrate, and a large tumulus near it, has been added by 



1 Continued from p. 518. 



