56 



NA TURE 



[November i^], 1892 



Planing is very common, and is either fl^t or with a 

 hollow or a convex surface. Some of the intensely hard 

 hornfels blocks have been ground on one or more sides, 

 several planes being sometimes ground on the same stone, 

 while some very hard rocks are deeply grooved. In other 

 cases the striations and scratches are so fine as only to 

 be seen with a lens ; while one surface block of very hard 

 material has been ground down and polished, so that it 

 glitters in the sun. In fact, every form of surface-grinding 

 produced by recent glaciation appears to be here present. 

 The surface of the ground is everywhere strewn with 

 pebbles and boulders, the result of the washing away of 

 the finer materials of the conglomerate ; but, besides 

 these, there is a tract of about two and a half miles by 

 one mile near the centre of the conglomerate-area, on 

 the north side of Mount Ida Creek, which is rather 

 thickly strewn with large blocks, termed by the writer 

 " erratics," though they can hardly be erratics in the 

 sense of having been deposited on the present surface by 

 ice. There are forty-five of these blocks, which are either 

 of granite, sandstone, or quartz, and vary in size from 6 

 feet by 4 feet, to 20 by 1 5 feet. One of the finest, termed 

 "The Stranger," of coarse-grained granite, is i6| feet by 

 \o\ feet, and 5 feet thick, the estimated weight being 30 

 tons. It is planed and scored in a remarkable manner, 

 as are most of the other blocks. It is curious that beyond 

 this limited area only three or four large blocks are found 

 on the surface, while no pebbles or boulders derived from 

 the conglomerate are found more than a hundred yards 

 beyon 1 the present limits of that formation. 



A striking feature of the conglomerate is the great 

 variety of rocks present in it, seeming as if "the debris 

 of a continent " had been here gathered together. There 

 are an almost infinite variety of granites, syenites, 

 gneisses, schists, quartzites, sandstones (hard and soft, 

 coarse and fine), slates, shales, conglomerates, amyg- 

 daloids, porphyries, vein- quartz, red, yellow, and grey 

 jaspers, and many others. Some of these can be identified 

 with existing rocks, but others are not known in Victoria. 

 In some cases there is what appears to be river shingle, 

 in others the delicate scratches preserved even on soft 

 shale show that the material has not been exposed to 

 any denuding action. There are also sandstone beds of 

 considerable extent and thickness intercalated with the 

 conglomerate, indicating that there were alternating 

 periods of river or current action while the conglomerate 

 was being formed. 



The whole of the phenomena here briefly sketched 

 point unmistakably to glacial action ; in fact, there 

 seems to be hardly any part of Wales or Scotland where 

 such action is more clearly indicated. There are, it is 

 true, no moraines, because the period when the con- 

 glomerate was laid down is too remote, both newer and 

 older pliocene rocks overlying it in some places. In- 

 deed, from fossils found in shales overlying what appears 

 to be a similar conglomerate at Bacchus Marsh, south of 

 the Dividing Range, the writer of the report is inclined 

 to consider the whole formation to be of Palaeozoic age. 

 In one part of the area the bed rock is exposed, and this 

 is covered with abundant striations crossing the stratifi- 

 cation lines, indicating either powerful glacier or iceberg 

 action. 



A list of localities where similar conglomerates have 

 been found is given, showing that they occur to the north- 

 ward for about 250 miles along the foot of the hills 

 bordering the Murray valley, disappearing under the 

 Tertiary deposits of the lowlands ; they have also been 

 met with forming the floor of the auriferous deposits in 

 mines at Creswick and Carisbrook, on the northern slopes 

 of the Dividing Range ; and also, as already stated, at 

 Bacchus Marsh, and a few other localities on the south 

 side of the range. We are not told, however, whether 

 similar indications of glacial action occur in these 

 localities. If these deposits are really all glacial and 

 NO. 1203, VOL. 47] 



contemporaneous, they indicate an extent of glaciated 

 country that would imply either a very lofty mountain 

 range or the occurrence of a real glacial epoch in the 

 southern hemisphere. 



The direct evidence of the superposition of Tertiary 

 rocks of Pliocene age shows that the glacial conglomerate 

 itself is of great antiquity, but no special attention ap- 

 pears to have been given to the question of the age of the 

 so called "erratics." The fact that they are found in so 

 limited an area seems to show that they are not derived 

 from the conglomerate itself by the process of sub- aerial 

 denudation, and the same thing is indicated by the 

 apparent fact that they all rest upon the present land 

 surface. The photographs seem to indicate this, and 

 nothing is said about their relations to the subjacent 

 conglomerate, or whether any considerable proportion of 

 them still form part of it, merely protruding above the 

 surface, as would certainly be the case if they owe their 

 present position to the mere washing away of the finer 

 parts of the deposit. But, if so, why should they be called 

 " erratics," as distinguished from the blocks and boulders 

 which are still embedded in the formation? If, on the 

 other hand, they are supposed to be true erratics— that 

 is, to have been deposited on the present land-surface by 

 ice agency — they must clearly be much less ancient than 

 the conglomerate itself, or they would hardly retain such 

 fresh-looking striations, grooving, and polishing as some 

 of them exhibit. It is to be hoped that these most in- 

 teresting deposits will be the subject of very careful study 

 by Australian geologists, since they seem calculated to 

 throw much light on the geological history of the old 

 Australian continent. Alfred R. Wallace. 



ON THE WALKING OF ARTHROPODA. 



IN a letter to Nature, published January 8, i8gi, I 

 described the manner of walking of several insects. 

 Recently I have been able to examine a greater number 

 of Hexapoda, together with several Arachnida and Centi- 

 pedes, and a few Crustacea. The results of most of these 

 observations were communicated to the Royal Dublin 

 Society a few weeks ago. 



I stated in my former letter that most usually the 

 insects examined moved three legs, e.g. the ist and 3rd 

 on one side, and the 2nd on the other, almost, but 

 not quite, simultaneously. In some insects it is the most 

 anterior leg of this tripod which is raised first ; in others 

 it is the most posterior. An example of the first case 

 is the cockroach, and of the second the blow-fly. But 

 again exceptions appear to occur in each case. This 

 almost simultaneous raising of the "diagonals" is 

 shown by observations, photographic and otherwise, to 

 be the rule in all the adult Hexapoda which I have 

 examined, except the Thysanura. Of this last group I 

 have observed Tomocerus longicornus, and find that, 

 while it often moves by the simultaneous use of the 

 diagonals, it also often raises its opposite legs simul- 

 taneously in pairs, especially when the animal is walking 

 on a smooth surface, and using the sucker which is 

 placed on the anterior part of the abdomen. 



This use of the opposite legs in pairs was also found 

 very frequently, as well as the diagonal walk, in the larva 

 of one of the Coleoptera, and is always to be observed in 

 caterpillars. Thus it is interesting to find that in one 

 species at least of the Thysanura, which are re^^arded as 

 having preserved many of the characteristics of primitive 

 insects the adult walks in the same manner as the larvae 

 of other insects. 



It is to be observed that those insects which have long 

 antennae move them, and apparently the maxillary palps, 

 in accordance with the diagonal rule ; for when the front 

 leg of one side is moved the antenna of that side is 

 twitched. 



