VI C TOR I A.
GEOLOGICAL SURVEY.
REPORT OF THE GEOLOGICAL SURVEYOR
ON THIil GEOLOGIOAL STRUOTURE
OF THE
~,or,onJ! ,of Vittoria,
THE BASIN OF THE RIVER YARRA, AND PART OF THE NORTHERN, NORTH EASTERN, AND EASTERN DRAINAGE OF WESTERN PORT BAY;
WITH PLANS AND SECTIONS.
LA! D upon the COmWIL TABLE by THE SURVEYOR GENERAL, by command of HIS EXCELLENOY THE OFFIOER ADMINISTERING THE GOVERN~fENT, and ale REPORT ol,del'ed to be printed, and the PLANS AND SEOTIONS to be lithographed, 5th j}[al'ch, 1856.
16n ~utbOtit)1: JOHN FERRES, GOVERNMENT PRINTER, MELBOURNE. A.-No. 108.11. 1
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1 Surveyor General's Office, 20th February, 1856.
SUI., I have the honor to submit to your Excellency the valuable yearly report of Mr. Selwyn, the Geological Surveyor. The withdrawal, on grounds of economy, of Mr. Selwyn's Field Party during 1855, has narrowed very considerably the field of his observations, but I hope that with the progress of the more detailed Topographical Survey, and the provision made by the Legislature for the Geological Survey for the current year, which will enable two survey parties to be engaged, a very considerable progress in our geological knowledge of the province will be effected. The advantage of a minute description of the highly interesting organic remains of the palreozoic' and o~her formations, and without which the researches of the geologist are ,incomplete, leads me to submit to your Excellency th~ importance of obtaining for this object the services of Professor McCoy, now resident here. I am aware that this eminent palreontologist is to a certain extent engaged in these observations; but I would suggest, that they should be made rather the subject of public than private investigation, and thus become national property. Professor McOoy has expressed his readiness to undertake this task. The means at the disposal of the Government, sanctioned by the Legislature, will cover the cost of this undertaking, without impeding the progress of the survey in the field. I have the honor to be,
Sir,
Your most obedient Servant,
(Signed) AND. CLARKE. _His Excellency , Major General Macarthur, &c., &c., &c. " REPORT
ON THE GEOLOGICAL STRUCTURE OF THE COLONY OF VICTORIA, THE
BASIN OF THE RIVER YARRA, AND PART OF THE NOR~HERN~ NORTH EASTERN, AND" EASTERN DRAINAGE OF WESTERN PORT BAY.
THE geological IIJap accompanying the present report embraces the whole of the area previously surveyed and reported on, as well as the districts lying south of the great east and west dividing range between the waters of the Murray and those emptying into Port Phillip and Bass's Straits, which have been examined up to the present date; the former with numerous additions, and corrections made from subsequent observations. By the' insertion of copious geological notes, with local descriptions of strata whenever the rock is exposed in situ, and the careful delineation of the boundaries of the several formations, I have end!?avored to render the map in itself, together with the illustrative horizontal section, as complete a geological report of the country surveyed as it is at present possible to make. The section has been levelled and measured ,Vith theodolite and chain the entire length, and is protracted on a true scale, horizontal and vertical, six inches to, one mile; thus the actual outline and elevation above the sea level of the country passed over is correctly represented, and the approximate thicl~ness of the exposed strata ascertained. The, comparative smallness of the area as yet surveyed, the small scale, combined with, the topographical incompleteness and errors* of even the best existing map of the Colony, and especially the want of a minute examination and Classification of the organic remains which have been collected from various localities, preclude the possibility of at present making any more minute sub "divisions of the several stratified formations
than has been ad O::i::O~'~~: Te";,ry { ~plVIl~~~~:ne , elOeene Pleistocene. Mesozoic-Secondary? Carboniferous of Australia. Devonian Palreozoic--:-Primary Silurian { Cambrian. A more extended knowledge of these formations and of their organic contents will, I have no doubt, eventually shew them to be susceptible of many of the recognised sub-divisions of their equivalents in Britain and other countries. The districts now under consideration are, both in geographical position and geological features, directly connected with those described in my last report, and are, in fact, exclusiv~ly occupi<;cl by the extension north and east of several formations .there noticed. ' Such being the case, only a brief recapitulation of their general.
.. This obstacle is however now being rapidly diminished by the very beautiful topographical maps of' various districts of the Oolony in course of construction by the officers. of the SurveY9T General's Dep!lrtment. GEOLOGICAL REFORT-b. 6
geological eharacter, as there given, will be necessary, at the same time noticing such changes or new features as have been observed either in the general relations to each othe1'.of the several formations, their local lithological characters, or in their mineral and organic contents. A glance at the aecompanying lllap will afford fuller, more accurate, and more detailed information than could be conveyed by many pages of letter-press, as well regarding the relative area occupied by the several formations ns the localities in which they are chiefly developed. . . This, however, does n.ot apply to the superficial pleistocene deposits, except where . they ex~st in Sl10h thickness and extent as to render the character of the subjacent rock uncertain, as is the case in. the Carrum Swamp, on the east side of Port Phillip Bay, and Koo-wee-rup, or the Great Swalllp north of vVestern Port Bay. ' ~
I ...:-,sTRATIFIED, AQUE;OUS, AND SEDIMENTARY..
1. CAINOZOIC 011 TERTIARY. a. Pleistocene {Alluvial and Di!u~ial drifts, and recent upheaved beach and estuary deposlts. Thickness, Range, and E:1:tent.-These strata may be seen in natnral sections from a few inches to twelve. or fifteen feet, and 'have been proved by boring and sinking to reach in some localities a thickness'of thirty feet. There is, lwwever, no reason to suppose this to be the maximum thickness which they anywhere attaiu.. In the.worked portions of' the Yarra gold fields (Caledonia) the average thickness of the diluvhtm never exceeds, and rarely re.aches twenty feet. In other gold fields it has been proved tD attain a thickness of 190 feet; at 170 fect fossil trees have heen discovered only very slightly mineralised. The specimens I have seen present the appearance and fracture of charcoal. In range and extent the pleistocene deposits iriRy be· said to be universal, as scarcely a' single square mile of country exists over some portion of which OIle or more .of. them could not be detected. For this reason it becomes impossible, without a map on a very, large scale, to define their limits; I have, therefore, as before stated, attempted to do so only where they attain considerable thickness and extend without interruption . over a large area. The most extensive tract of this description occupied by alLuvial and estuary deposits extends east fi'om Port Phillip Bay to the base of Strzlesld's Range, embracing the Carrum and Roo-wee-rup, or Great Swamp, the two being connected by a narrow band of low lying swampy country, in which the waters of the Dandenong, Eumemmcrring, and Gard,iner's Creeks are lost, .only finding their way to the sea in seasons of flood, either through the numerous tidal inlets at the head' of \;Yestern Port, or through the sandy bars at either end of the Nine-mile Beach. . . Many parts of this' area' are, I believe, still beneath the sea level, the water having been excluded from them by the successive terraces or. beaches of sand, which have beell, piled up by the cDmbined action of wind and waves, and now form the narrow' sandy belt diviqing the Carrum Swamp from the sea known as the Nine-mile Beach. . A depressiDn of fifteen Dr twenty feet would be sufficient again to submerge the whDle of the above area, and to connect the waters of Port Phillip and "\Vestern Port, as was undoubtedly the case during some portion .of the pleistocene pel·jod..'. . Along the entire coast· line from "\Villiamstown to Cape Patterson, including the shores. and islands .of Western PDrt, remains of a raised beacl~ 7 of the pleistocene period occur at intervals, the' greatest elevation above the sea level at which it is now found being nearly 300 feet, and in some ., instances as much as four or five miles inland. Two instances have occun'ed in which a single fragment of shells (ostrea and haliotns) apparently belonging to this period, have been discovered at a much greater elevation: the first on Monnt Blackwood, by Bryce Ross, Esq.; and the second on the flanks of River Hill, in 'Vestern Port, by my assistant, Mr. Daintree, in neither case at an elevation less than 700 feet. From the position in which these fragments were found, at or very near the smface, it is not impossible that *ey may have been conveyed there by aborigines. . MINERAL AND LITHOLOGICAL CHARACTER. 1. Estuary and Littoral Deposits.-Accumulations ill stratified beds and layers passing into each other of fine and course siliceous, white, and black sand with shells; stiff blue, yellow, brown or mottled clays, and black mud with a few shells and carbouised vegetable matter. III the clay, interspersed with numerous shells of recent species, sulphate of lime is found in abundance in various crystalline forms and sulplmret of iron in small quantities. These clay beds have been cut into and well exposed on the line of the Melbourne and Mount Alexander Railway across the swamp north-west of Batman's Hill. The sulphate of lime does not occur in sufficient quautities to be of any economic value, nor do any valuable minerals exist in these beds. 2. Alluvium and Diluvium (aurijerous dl'ifi.)-'-Accumulations of sand, gravel, clay, and large subangular and partially or much rounded fragments of quartz, sandstone, or quartz rock, &c., occasionally in distinct strata,'but more often forming a confused and irregular mixture of detritus of all the subjacent rocks, the largest fragments invariably occurring with the gold most abundantly towards the lowest portion of the mass. 'With the exception of clay for brick making, which is almost every" where obtained from these beds, gold is the only valuable product derived fi'om them. Menaccallite ortitaniticit'oll and magnetic iron in the form of fine sand and gravel also occur in considerable quantities, but are of no economic value. These auriferous drifts, or pleistocene deposits, in which 1110re or less of the precious metal may be found, are almost co-extensive with tIle area occupied by palmzoic strata (colored lilac on the map), and extending north from Gardiner's Creek to the Di.viding Range between the waters of the Yarra and GOlllburn, and east from the Plenty to the jnnction with the YalTa, of the Badger Creek and the 'Yorri Yalloale Owing to the dense nature of the country and the small staff (two men) at my disposal, I have been able to penetrate only a few miles beyond the abovcnamed points, and in that distance no change in the geological nature of the country was observed. I may here mention, the country drained by the 'Yoni Yalloak on the north-eastern flanks of the Dandenong Ranges, as being especially likely, from its geological features and the abundance of quartz, to prove highly auriferous . .All the creeks 011 which gold was found to exist during the progress of the survey, or has since been obtained by the miners, have been indicated on the map. The existence'of these auriferous tracts to the north of the River Yarra was reported by me to the Colonial Secretary in a letter dated 31 st August, 1854, enclosing two small samples of gold obtained. during the progress of the survey in those districts, in which, at that period, no auriferous deposits had been worked or were known to exist. 8 , In 1;his and other parts of the, Colony the following minerals have been found in these dep9sits, most, if not all of them derived from older ·rocks: GOLD, Argentiferous. L1ME, Carbonate., TIN, Native, " Sulphate. " Oxyd. JJAZULITE. GALENA (Sulphurot of lead). TOPAZ. ANTIMONY, Sulphuret. SAPPHIRE. IRON, Oxydulated magnetic. SPINEL•. " Titanic. ZIRCON. " Chroic. QUARTZ. " Sulphufot. " Arsenical. " Hrematite. Origin and, Probable i.1{ode of Accumulation. -The irregular and confused mixture of angular and rounded detritus which, as already noticed, forms so large a part of the drift formation, is such as one can harcUy imagine could be the result solely 0f marine and fluvifitile fiqueous fiction. "Whether ice has here, fiS in other countries, played .an important part in the distribution of these drift deposits, is a question on which no satisfactory evidence has yet been obtained. . Their general similitude in geological character to those of other countri~s, which are now proved, to be the resulti of combined glacial and marine aqueous action, leads one to .imagine that some similar cause may have operated in this country during the drift period. The chief objection to this glacial theory as applied. to this country, appears to exist in the general, if not total absence from the drift 'of any distinctly transported fragments; and furt.Iier, that whenever the subjacent geological formation changes, an equivalent change is immediately remarked in the sllperincumbent drift: thus in the amiferous drifts, which in every district I have examined, invariably rest on a more or less decomposed schist, shale, clay slate or sandstone bottom. I have never been able to detect fragments of the granitic or basaltic rocks which may be in the vicinity, and the drifts of the granitic and basaltic districts, 'at least in the western and central gold fields, contain neither fragments of the palreozoic strata nor any trace of gold. In the present state. of our knowledge regarding the formation of these deposits, the actual productive value of any given area iIi which they exist, and where they hfive been proved to contain gold, in however small. a quantity, can only be accurately ascertained by working. Such being the case, so long as the present system of working ill small parties is continued, there must filways be an enormous amount of, unproductive or very unequally remunerated labor expended. Due regard should, however, be always paid to the thickness, number, extent, and direction of any qUfirtz veins which may be found traversing such arefi, as these are, I have no doubt, the source whence all the diluvial gold has been originally derived. The proximity or otherwise of large masses of granite or other plutonic , l'ocks should also be tl'J,.ken into considemti9n, as they have, in fill prohability, had a considerable influence on the formation of the auriferous quartz veins. The only means by which'the present stfite of uncertainty regarding the value of these deposits might perhaps, in some measure, be dqne away, and geological facts elicited of real practical value in directing the labors of the mine!' to a successful issue, would pe the carrying out of a very detailed geological survey of the gold fields now being worked. ' . For this purpose fi good topographical mfip, on a scale of at least two inches to the mile, exhibiting all .the physical features of the surface, would be indispensable. Accurately measured vertical sections of the strata sunk through, over every part of the area, should then be obtained, and from these numerous horizontal sections might be constnwted; and in this way a grefit mass of geological information 'could be collected, which might ljrove of , . practical value, and would undoubtedly be of great scientific interest. ' 9
The more intelligent miners could easily render very great assistance in this undertaking, if they could be.induced to preserve aCC1'!1'ate measure ments of the thickness of the strata they are sinking through, with any other observations bearing on, their geological character they might 1l13ke during the progress of their work. . . Organic Contents.-In the diluvial auriferous drifts no .allimal organic remains have, I beli.eve, as yet been discovered. Trunks of trees, seed vessels, and fragments of wood have' been met with at various dept~s to 170 feet, at which depth a large tree was cut through on the Balluarat $old field. . In the ·raised beach and estuary beds numerous shells, chiefly, if not entirely, of existing genera and species, are found interspersed or forming beds in the sand and clay. . . The most abundant of these are: Qstrea, NIytilus, Area, Patella Halio tus, Turbo, Trochus, Natica, &c. . Layers, .several inches. thick, almost entirely composed of fraginents of Mytilus, in .loose black sand, are of fi'equent occurrence round the coasts. b. Pleiocene } .. c. Meiocene Tertiary. d. Eocene Thickness, Range, and E:dent.-.-These formations exhibit in one locality on the shores of Port Phillip, a thickness of about 200 feet; and along the course of the River Bass, east of Settlement Point, nearly 100 f€et.· In neither instance are the lowest beds exposed, nor is the whoJe series present. The range of these beds is entirely confined to the vicinity of the present coast line, and only in one or two instances, viz., in the valleys of the Dal'ebin Creek and the Plenty, and above the Diamond Creek, ilear Eltham, appears to have qxtended as much as twelve miles inland. Vve have good evidence, however, in the numerous small outlines or detached patches found on Phillip Island, 'Vest Head, the west shores of Western Port, and north-east of Brighton, of their having at one time existed over a much more extensiveal'ea than they at present occupy. They also, in all probability, extend underneath the greatel: part of the llewer pleistocene ·estuary deposits. This has been proved to be the case between Batman's Hill aud the mouth of the Yarra, and they are seen surrounding nea.rl y on all sides both the Carrum and the Great Sw~mp. The best natural sections in tlwse beds are situated from Point Nepean to· Mount Eliza, from Mordialloc to St. Kilda, along the course of the River Bass, and in the neighborhood of Flemington. , . ,- Geological Position.-Resting, unconformably, on all the older rocks, whether stratified or igneous, and are, though in some inst.:'lnces as much as 400 feet above the present sea level, always, a few cases of local distlU'bance excepted, either horizontal or dip at very small angles-lo to 5°. Mineral and Litlwlogical Character .-1. Loose sands, very soft friable red sandstone, ~lnd coarse gritty or gravelly beds with. bands of small quartz pebbles, calcareous nodules and veins occur in the sandstones, probably carbonate of lime, and magnesia of an opaque white color; seen on many parts of the Brighton beach. ' . 2. Beds of very hard, blaci(, metallic-looking ferruginous sandstone, locally known as ironstone, and used both for building and road material. . The sand is always silicious, with a ferruginous or felspathic cement, which varies in color from almost black to red, brown, yellow, and white. On the Bass are thick beds of soft white sandstone (freestone), in which the cementing matter is purely felspathic; these are evidently formed from granitic detritus. . 3.. Beds of stiff light blue clay, ¥lith b~nds and nQdules of greyish brown limestone, crystals of selenite (sulphate of lime ), and slilphuret of iron. occur in the day. Ironstone concretions, often assuming fantastic forms, GEOLOGICAL REPORT-C. 10 and presenting the appearance of ,having been melt.ed, are very numerous. They have, however, never undergone the action of fire, but ,have been 'deposited by infiltratioil in cavities once occupied by SOl'ne organic substance, or in cracks and fissu:res of the, sandstone. They are very' llUmerous along the Brighton beach and in the vicinity of the Red Bluff. , A singular bed, belonging to the tertiary series, 'of very hard white cherty looking rock (silicate of alumina) occurs resting on the granite of Mount Eliza, .immediately east of Cannanook Creek, and also in asmall gully near the beach. , It contains numerous remains of marine plants, and has been supposed to be limestone, and the fossil plants contained in it to indicate the existence of coal, with which, however, they have no connection. , , Origin and Afode, of Accumulation.-Whether these strata present :alternations of ,marine and fresh water deposits is at present uncertain, and can only be determined when a much larger area has been surveyed, and' "the organic remains from all the strata collected and examined. Mr. R. B. Smyth has, I believe, obtained s,ome evidence of the ,existellce ,of an alt.ernating fresh water deposit in the beds near ITlemington. . Organ'ic Remains.-These consist of numerous genera'and species of :mollusca, fossil wood· and leaves and stems of land and marine plants. ' The chief localities from which' they have been collected are-'' 1. Between .Mount Eliza abd Mount Mai,tha, east shore of Port :Phillip. Bay. ' 2. Brighton 'Cliffs, from Mordialloc to St. Kilda. 3. )?,etween Melbourne, Pentridge; Essendorj., and, the Saltwater River. Very few of the specimens have yet been examined, and I am there~ fore unable to furnish any corr.ect list of species. Most of the genera'.!' are found fossil in the London clay and crag
formations ofBritain. ' , . 0 • ' J.1fesozo'ic or Secondary Carboniferous qt Australia '(-'With regard to this formation I have at present very little more information than has "been given in previolls reports. " . With the exception of the small patches on French Island and Phillip Island, I have ascertained that the carboniferous beds, nowhere in the district now reported on, extend far to the west and north-west of the River Bass. They are in that direction cut off by basaltic anel other igneous rocks, the -actual junction of the two being covered up af).d totally concealed by a thick deposit of tertiary sandstone. ' On the north-west flanks of the Bass Range, River Hill, &c" we find the carboniferous sandstones and shales cropping in nearly all the ,creeks and gullies. They almost everywhere contain either thiri streaks of .coal, numerous vegetable impressions, or fragments of opalized wood. ,Such being the case, there is a probability of workable seams of coal existing in some part of these ranges, which are now covered with dense. forests and impenetrable scrub. This might easily be proved by a series of bore holes executed at proper intervals ~'om north~'west to south-east across the general strike of the beds. Should a seam of coal, however, be discovered; I m~ch d'oubt,con~ sidering the present low' price of that aI!ticle, the high price of labor and . materials, and the difficulties of shipment that would have to be encountered, whether it could now be worked to advantage. . Freestone, lilentioned in a' former report as -existing in abundance at -Griffith's Point, is now being quarried and shipped to Melbourne. No trace of fossil fauna has as yet been discover,ed in the carboniferous strata in Victoria. rhe fossil flora is considered by Professor McCoy to be
,. Ceritliium, &alaria, Pnrpura Cancellaria, Nassa, Ovula, Cyprea, Vol uta, Erato, Littorina, Patella. :HaIiotus, Nautilus, Spatangns, Dentalium, Pecten, .Area, Nucula, Donax, Tellina, Lima, :rerebratula, .Anomia. 11
-of an oolitic type, and thus it is at present uncertain whether these coal bearing strata are of mesozoic or palreozoic age. This is an interesting brown .banded shales and sall<;!stones j ' in which only a few indistinct traces of fossils .are visible, and then the thin calcareous bl'eccia beforementioned, about six feet in thickness, and very full of organic remains similar to those abovementioned, but both more plentiful and more perfect than in the uuder lying conglomerate; it is usually of. a rusty brown color, with a Tough vesicular aptlearanr:e' on the surface i but where the atmosphere has not acted on it presents a s'olid (wystallil1(~ structure, and of a blue color, dotted with distinct crystals of clear' and opaque white carbonate of lime. This bed much resembles some of ,the calcareous volcanic ash beds of the silurian rocks of.Brit:ain. ,81;11a11 plates of silvery and d!1rk colored mica are also seen 'in it, but , 'are most abundant in the underlying conglomerate and sandstone bands. Distinct thin VEins of white quartz traverse the calcareous breccia, and are frequently seen intersecting sQme delicate organic remain. . 13 The beds are dipping from 300 to 45 0 east and west, and owing to the undulations in them recur more than once on the surface. In attempting to trace out these contortions or the extension of the beds in the direction of the strike, they are found to be constantly and completely covered up and con cealed by superficial alluvial and diluvial deposits. About six miles north of the Yarra, on 'Watson's Creek, and on the direct strike of these Anderson Creek beds, we find slightly calcareous hard grey fine grained sandstone, with many similar fossils. Again, twenty-four miles further north in the same direction, viz.: N. 150 E. on the Muddy and Murindil1de Creeks, tributaries of the Goulburn, calcareous strata, with similar fossils occur. In the intermediate country I have not yet been able to detect either the peculiar conglomerate band of Anderson's Creek, or any fossiliferous or calcareous beds C; with this exception, the general geological and mineral character of the strata is the same throughout. Organ'ic Remains.-Numerous palreontological, as well as lithological specimens have been collected from all these beds. None of the organic remains have as yet been fully examined. Subjoined is a list of some of the genera and species given me by Professor McCoy, from a very cursory examination he made one afternoon of a few of the specimens in my possession. Many of them have, I regret to say, been lost or much injured from the want of any proper accommodation for them. ZOOPHYTA. Ptilodictya fucoides-GoulbUl'D. Favosites. Fenestella, 2 sp.-Yarra. ECHINODERMATA. PI'otastel', 1 sp., new-Melbourne. Asterias, :2sJ?-Melbourne and Upper Yarra. Petmia, :2 sp.-Upper Yarra. Actinocrinus.-Uppel' Yarra. INCERTE SEDES. Pleurodictyum, new -Upper Yarra. CRUSTACEA. Cal yniene tu bereulata-Uppe]' Yarra. Cheil'Ul'us, new-Upper Yarra. Sphrerexochus and others uncertain. LAl\1ELLI BHANCHIATA. Arca '? Avicula, 2 sp. BRACHIOPODA. ~, Atrypa l'eticulul'is. Lrnptena minima. Strophomena umhraculum. Ling'ula Or-this Pentamerus, 2 sp. Siphonotreta. GASTEHOPODA. Loxonema, 2 sp. Mul'chisonia, :2 sp. c'EPHALOPODA. . Orthoceras. PTEHOPODA. Theca. These specimens, with the exception of Ptilodictya, have all been collected from different parts of the Yarra basin,· from Melbourne to about forty-five miles up the river in a direct line. ~ In what appears to be the lowest exposed portion. of the series, viz.~ the beds 011 the DIamond Creek, no organic remains have been detected. GEOLOGICAL REpORT-a. 14' n.-IGNEOUS, PLUTONIC, AND VOLCANIC. 1. BASALT, LAVA, AND OTHER PLEisTOCENE VOLCANIC ROCKs. Thickness, Bange, and Extent.-The. country occupied by this fOrli1a tion il3 exclusively confined to the north of the River Yarra, apd, with the exception of a portion of its course near ·the Yan Yean, to the ,Yest of the Plenty. In the latter direction it extends over very large areas, but has not as yet been examined anywhere west of the Sydney Road. . AloJ;lg the course of the Plenty, where good sections of it are exposed resting on the upheaved and denuded edges of the palreozoic strata, it rarely attains a thickness of fifty feet. It ilOW forms a perfectly level country with a gentle slope to the sea level from a height of about 700 feet on the Sydney Road and Merri Creek; it has, however, flowed overah undulating. or hilly surface, and the. thickness of it.in any given locality will of course depend on the uildulations of that original surfac~. Thus in the deepest valleys of the old surHwe the greatest thickness of lava now exists. On the line Of section it will be seen that whenever the old surface rose to a greater elevation than about 700 feet neal' the Merri Creek, or about 500 feet on the River Plenty, the lava stream has' thinned out, and the older rocks, w~lich at lower levels are covered up, are in SllCh cases still exposed on the ~li.r!ace, this' high grol!ud having formed islands in a sea of lava. . Decomposition and denudatIon has, in all probability, much reduced the original thickness' of the lava, and perhaps. the exposure of some of the hills of palreozic st rata above allu'ded to is partly due to this cause. Geological Position and Age. -Resting horizontally on all the older I'oelts, whether igneous or sedimentary. That they are of \Tery recent date,· probably the close of the pleistocene. drift period: is best proved by the fact of their nowrestillg in many places on pleistocene auriferous drifts and other tertia:ry strata. . LithOlogical Character and A1ineral Contents.-Hard crystalline columnar basalt (augite felspar, iron, and olivine) very vesicular, the vesicles commonly either filled or coated with opaque white carbonate of lime with a silky"'lustre. This character is applicable to by far the greater portion of the mass. Interstratified with it are other beds, having either a globular concretionary or a polygonal structure. In the accompanying rough sketch (Fig. 2) of a section seen ·on the Campaspe I have attempted to illush'ate these differences of structure. .' In some places large quantities of red and black scoria., very porous, and occasionaUy light enough to float on water; these are most common, if not entirely confined to the neighbourhood of the mammillated hills, many of which are seen rising from the lava plains.. . These hills in most instances bear evidence of having been the points of eruption whence the ,lava and scorire have geen ejected and constituted volcanic islands in the pleistocene sea. _ On the...£) green hill north of. IGnlochewe Inn, Sydney, Road, the ancient crater is still distinctly visible. Several other and smaller hills of the same character, but on which no crater~form cavities are visible, occur near the source of the Merri Creek; and there is little doubt that these hills are the true source whence the whole of the basalt or lava which now occtipies the country between the ~lenty,. the Yarra, and the Sydney Road has .been derived, and certainly not, as has been suggested, from the swamp west of Batman's HilL* ,. Transactions of the Philosophical Society of Victoria, vol. 1., page 229, c. 231. ·15 No minerals of economic value have, I helieve, heen found in this formation. Native antimony lias been repol~ted as having beeil found in a cavity in bluestone on the Merri Creek, and carbonate of copper on Jackson's Creek. In the latter locality I have ·been unable to find the slightest evidence of such being the case. The most common minerals are:- Sulphuret of iron. Carbonate of lime. Carbonate of magnesia. l\1csotype. Olivine. Varieties of common opal or hydrated alica. Siliciferous hydrate of alumina. Soapstone. 2. BASALT, AMYGDALOID PORPHYRY AND OLD ERUPTIVE ROCKS. Range and Extent.-The largest area occupied by these oldertmppean and basaltic rocks is situated Oil the south, east, and west shOlfes, including the islands, of vVestern Port Bay. Small isolated patches are also found in the following places: Mount Ararat, on the Gil:;ps' Land Road; on the Eumemmerring Creek, in the parish of Berwick; on the W oori Yalloak, in the parish of Yering; and at the Kangaroo Ground, north of the Yarra. The western portion of the city and suburbs of Melbourne, including Emerald Hill, Batman's Hill, Flagstaff Hill, the Benevolent Asylum, and Flemington also stand on portions of the same formation. Cuttings and excavations have recently been made in it on the line of the Mount Alexander Railway, and also in laying the gas and water pipes in Melbourne. Geological Position and Age.-They have been erupted in the positions they now occupy through both the granitic and the palreozoic and mesozoic? or carboniferous strata, and unaltered tertiary strat.:'1 are found resting on them. They are therefore older than the tertiary and more recent than the carboniferous fOTIllations. , Litlwlogical Character .and 111ineral Contents.-Thick masses of very hard dark, almost black angitic basalt or ironstone, often vesicular and columnar. " Bands eight or ten feet thick of very soft red, grey, greenish brown, or white clay often presenting an amygdaloidal pOI1)hyritic or marbled appearance. The present soft state of some of these bands appearS"- to be the result of a general decomposition of the mass of the rock, as even in the softest portions the original crystalline. structure can be still detected. Great numbers of globular concretions of hard black basalt and mammillated or concretionary masses and veins of iron hrematite are still found imbedded in or traversing the soft decomposed mass. The basaltic concretions decompose in concentric lamellar coats, the decomposition gradually lessening towards the hard internal nucleus. The soft amygdaloidal porphyritic and marbled beds before mentioned never pre~ent the slightest appearance of crystalline structure. Fragments on exposure become har.der and have a dull earthy fracture. Varieties of siliciferous hydrate of alumina appear to be the mineral with which the vesicles or cavities in these argillaceous beds are filled: it occurs from pure white through yellow to brick red, the base being of a dark red bluish grey, or rusty brown color. The shores of Phillip Island, Cape Schanck, and vVestern Port, are the only localities where I have seen beds of the last described character exposed. Unlike the more recent basaltic formations in which, as before stated, the columnar and polygonal stru9ture is most prevalent, we here find the concretionary predominating, and never see, any of those very light vesicular scoria: which are indicative of subrerial volcanic action. On the outskirts of the small isolated patches in the Yarra basin 16 masses of very hard quartz rock occur,apparently due to the alteration of the palmozoic sandstones in .contact with them at the tim.e they were erttpted. . . With t.he exception of the h:oematite iron ores, which in some parts of the area occur inconsiderable quantity, no metal or mineral of economic value has been discovered, nor h~ve I seen any trace .of the existence of such in this formation. The white clays are u~ed by many of the settlers as a substitute for lime in whitewashing. The following minerals occur :-. Iron, Native. }} Sulphuret. }} Red and brown brematite. }} Black oxyd magnetic. Zeolite, varieties. Opal-Hydrated silica. Kollyrite-Silieiferous hy,drate of alumina. Olivine. Carbonate .of lime. Fluate of lime. Carbonate of Strontian. ;From the smalle:t: masses of this formation no good building .stone· ~ould be obtained, and none exists in it equal in quality to that obtained from the more recent basalts. The hard concretionary nodules afford excellent road material. . . o 3; GRANITE, FELSPAR, PORPHYRY, SYENITE, OR PLUTONIC ROCKS. Range and E.vtent.-The principal areas occupied by these rocks occur north and south of the River Yarra, with an intervening tract of palmozoic strata through which the river flows. Higher up the river, to the eastwal'd, these granitic and porphryritic masses are, in all probability, con nected witli each other and form one continuous mass with the great granitic chain of the Australian Alps. In this direction, however, the country. is covered with dense forests and scrub, and without cutting a road is quite impenetrable. On the north side of the Yarra all the highest points of the lllain .Dividing Range, between the waters' of the Goulburn and the Yarra, are composed of these rocks, .viz: Mount Despair, Mount Monda, Mount St. Leonard, and :Mount Riddel. About six miles south from the1ast named point the bou:ndary of the granite makes an acute angle, and runs about E. 10° N., following the course of the Yarra to the Gap, beyond which point I have been unable to penetrate. On the south side ·of the river they occupy an extensive tract of country lying east of the Dandenong Creek and north of the Gipps' Land Road, extending to' the culminating point of the main east and west. Dividing Range, between the waters of the Yana and those flowing to Western Port Bay, including also the whole of the Cor~han-warabul, or Dandenong Ranges, the highest point of which is 2450 feet above ~he sea level. About two miles west of Mount Ararat they cross the Gipps' Land Road and then disappear to the south under the alluvial soil of the Great Swamp. To the east of Mount Ararat no other rocks than granite are seen on the line of the Gipps' Land Road for upwards of twenty miles. Thi.s district has not yet been examined. . . In addition to the above many' other small patches of plutonic rocks are seen in the district embraced in the accompanying map; such as Cape Wollamai, Arthur's Seat, Mount Mal:tha, and Mount Eliza, noticed in my last report; also at Janefield, on the Plenty. Elvans, or felspar porphryries occur in the form of narrow dykes or bands cutting thro~lgh and upheaving the palmozoic strata at various points in the Yarra basin.' These are most of them indicated on the accompanying map: . , 17 Geological Position and Age.-With few exceptions these plutonic rocks constitute all the main water sheds and highest ranges of the district. They have upheaved and metamorphosed the palreozoic strata on their fl~nks, and have therefore been intruded since the deposition of the latter. Whether the granites and porphyries are of different periods, or only accidental modi fications in mineral character of the same mass, is uncertain. They often appear to pass into each other, but small isolated patches of the porphyry, as well as branches from the mass, are found penetrating the granite, which is not found similarly intruding in the porphyry; and we might therefore imagine· the porphyry to have been erupted at a perjod subsequent to the formation of the granite. . Lithological Character and Minerals.-The granite presents numerous modifications in lithological character, dependent on the relative proportions of the quartz, felspar, mica, hornblende, or schorl of which it is composed. The most common form is a true ternary granite, or composed of equal pro portions of the three first-named minerals. On Mount Despair it assumes a laminated ~ppearance, like gneiss and consists chiefly of felspar and mica, with schorl and very little quartz. The northern portion of the Dandenong Ranges is composed of varieties of felspar and quartz porphyries, the latter. being very similar in color and mineral composition to the old eruptive masses of quartz porphyry in Caernarvonshire, North vVales. . . It is of a light pinkish brown color, passing into grey, and when closely examined appears to be composed of numerous small felspathic fragments rather than crystals, of green, pink, red and brown color, with distinct interspersed crystals of clear quartz, the whole forming a very hard compact rock. In other places it is a very hard, dark blue crystalline felspar trap, studded throughout with brilliant plates of black mica, crystals of glassy felspar, and occasional specks of sulphuret of iron. Some of the felspathic or elvan dykes are studded with sulphuret of iron in small cubes, also crystals of double hexahedral quartz. I have been unable to find any minerals. or metals of value in the plutonic rocks of this region, and the only minerals I have seen in them are .those which form a constituent portion of tho rock. Specimens illustrative of the different .characters of all these rocks have been collected. They are at present in my possession, but will, I hope, ere long be deposited in the Museum of the Melbourne University, where t~ley will, ~th all others collected by the Geological Survey, be open to the inspection of the public. . General Rema1'ks, P h,ysical Feat'ltres, Soils, Water, o/c.-The physical features of a district, as well as the supply of water and its agricultural character, are always more or less influenced by the nature of its geological formations, and this remark applies in more than the usual degree to nearly every district I have visited in this Colony. Those districts occupied by tertiary strata (alluvial and diluvial deposits excepted) are generally flat or gently undulating country, lightly timbered with stunted Eucalypti (peppermint and mess mate) and'a prevalence of honeysuckle and she oak, banksia and casuarina, with an undergrowth of coars~ grass, fern, heath, grass tree, and varieties of prickly scrub, on a poor, loose, sandy or clay soil. In and on the borders of those low lying portions, which are covered with alluvial deposits, and are for the most part under water during the winter, a rather rich black sandy peat soil exists, which, when drained, is well adapted for agriculture. In such localities the country is well grassed, and timbered with fine red gum, cherry, and lightwood trees, (Eucalyptus, Exocarpus, and Acacia Melanoxylon), the luxuriant growth of the latter being an almost' invariable accompaniment of a rich soil. Fresh water springs are found in some parts of the tertiary area, but GEOLOGICAL REPORT-e.~ . 18 are of .rare occurrence,' and the chief supply of water is obtained from surface drainage collecting in swampt31 lagoons1and artificial resel'voirs. 'tVells sunk to a depth of between thirty and forty feet afford a . constant supply of beautifully clear watel\ commonlY1 howeveI\ so strongly imi)regnated with salts as to be unfit for drinking or other domestic purposes. 'Vhat the nature of these salts ai'e, or whence derived, I have been unable to ascertain. - . , Muriate of soda, sulphate of magnesia, and alum, are ,probably the most prevalent. Cat~le are fond of this water, but most horses'refuse it, unless much pressed by thirst, 'and then drink only spariI:lgly of it. .It varies very much in quality 'Within short distances, and in some few cases is so slightly saline as to be fit for drinking, though not pleasant to· the taste. Fresh water in small quantity _can be obtained almost anywhere on the 'coast, by sinking a shallow ~hole in the sand, a few feet . above high water mark. . . The area occupied by palreozoic strata consists chiefly of' steep ranges and gullies, often thickly and almost exclusively timbered with stringy bark,. , which rarely, except at considerable elevations and in the vicinity of plutonic' and igneous rocks,attain any great size. ,Occasionally a few she oaks (Casuarina), cherry (Exocarpus), or wattle (Acacia), are interspersed, espe- dally on the lower ground.,_ , ' On. the borders of many of the creeks and rivers extensive .alluviaL flats occur, richly grassed and lightly timbered with honeysuckle; she oak," lightwood, cherry, and gum. The l)1ost extensive of these in the district are· situated on either side of the Yarra, in and north of the parish of Yering,. where some twenty 0'1' twenty-five square miles exist of very'rich agricultural land.' A large portion of this is un9.er water during tbe '\vil1ter floods, but perfectly dry in SUnll;ler', and might -be drained without difficulty. _ vVith the exception of these river fiats; no really good agricultural land exists in the area occupied by paheozoic rocks; a very scanty covering of soil is found on the higher ground, and is commonly 'a barren, sandy clay. Of all the numerous creeks flowing to the Yarra from north and south, between Melbollrne and the Gap, not one that rises in and drains an area exclusively occupied by. palreozoic strata, is a p~rmanently running . stream; whereas a11 those rising ·on the plutonic rocks; even if their course .be less than half the lengih of the former, ilivariably flow throughout the year. ,'. ' . Of the former we find, on the north, Diamond, -W-atson's, View Hill, and Steel's Creek; and on the south, Deep 'Creek, Anderson's Creek, Brushy Creek, and others unnamed, draining together an . area of not less than foui' hundred square miles. .Of the latter we. have the Plenty, W"atts' River, Badger Creek, and the Don, on the north; the 'Vo1'1'i Yalloak, Yarra Rivulet, and others, on the ·south~ . The difference in the annual amount of rain fall and evaporation -on the higher densely timbered, and the lower and more open ranges, is not alone sufficient to account for this' phenomenon. The canse of it must therefore be, I think, in the-different absorbing and retaining powers of the i'ocks constituting the two formations. : . In the palreozoic strata the water i~ absorbed 'and _retained in the loose grained, porous sandstones, such as constitute large portions of this formation, and either. slowly exhausted by evaporation, or carried down the highly inclined beds to lower levels. Froll1 the compact crystalline structure of the plutonic rocks, little or no absorption or retention can take place, and the waters which- fall on the surface pass slowly through the joints and fissures which traverse such rocks ih all directions, and again appear on the surface at lower levels, in .the form.of springs. That a very great difference does exist in the absorbing power of these rocks is easily proved ?y imnlersing in water for a given time, and then 19 'weighing two pieces of previously equal weight, of the loose grained, porous sandstone above referred to, and hard, compact, crystalline porphyry, from the Yarra Ranges. On these hig~er ranges we almost invariably find a rich red or black . loamy soil, and a dense luxuriant and peculiar vegetation, never found on the lower sandstone ranges: enormous Eucalypti Blackwood (Acacia), Sassafras (Atherosperma), Beech (Fagus), Mountain Ash (Eheocarpus), Dogwood (Bedfordia), Hoppole (Pomadderis), Musk (Eurichia), Fern trees (Dicksonia and Alsophila), &c, . Near the highest point 'of the Dandenong Ranges, I measured one tree, which had been blown down, and found it to be 216 feet from the root to the first branch; and another was 18 yards in circumf~rEmce 3 or 4 feet from the ground. These were species of Eucalypti, I think white gum, and there were many more of nearly equal dimensions. That this peculiar vegetation is more dependent on moisture than on elevation or geological position is evidenced by the fact, that in many instances we find it extending from the high ranges along the borders of permanently running streams where sufficient soil exists, to within a few feet of the sea level. This feature is very marked on the. River Bass in V{estern Port, where it forms' a narrow belt on either bankof the river, extending for many miles through an otherwise open balTen country, covered with heath and prickly scrub, and a poor sandy soH, the detritus of subjacent 'tertiary strata. The richest agricultural lands of the district are always found in one or other of the four undermentioned geological positions :-. 1. As in all other c(luntries, on all river and other alluvial flats. 2. On the older basaltic formation. 3. 'Vherever two' or more geological formations meet, or are found interlacing each other, with the exception of granitic or palffiozoic strata. 4. In all the a,reas occupied by the recent basaltic lava or blue stone. Marked instances of No.2, occur at the Kangaroo Ground, in the south west corner of the parish of Yering and at Mount Ararat, on the Gipps' Land Road. In the first named locality the land has been cultivated for upwards of fou,rteen years, and always yielded abundant crops, without ever requiring a single load of manure. . As instances of No.3, we may point to the parish of Berwick, on the Gipps' Land Road; the entire district immediately north of Melbourne lying between Heidelberg and the Saltwater River, and also xhe course of the Plenty on the west side. . Though a large amount of good agricultural" land exists on the. recent ;" basaltic formation, it is frequently so thickly covered with loose stones and. blocks of lava, as to require a large outlay_ before it can be rendered fit for cultivation. " - This, from its difference in lithological' character, is never the case With the older basalt formation. Wells sunk in almost any part of the recent lava plains, would afford an abundant supply of water. The existence Of these waters ,vill always be found a severe check, if not a complete bar, to individual enterprise in workinO' the auriferous drift deposits, which, in many portions of the Colonv, undoubt: edly exist underneath them. _ .; In concluding these remarks, I must beg to observe, that any thin 0' contained in them, except where other localities are referred to, can be- take~ to apply solely to the area over which the labors of the O'eoloO'ical survey .have extended, comprised in the accompanying map. 1:> 0 " This, as compared to the whole Colony, is, I regret to say, exceedingly 20 small; and', therefore, it will not be surprtsing if some of the' views now expressed:, shoilld require' alteration or modification on su\lsequent observa tion over .distant portions of the Colony: a result which, I need har4ly sny, , 'has chamderised the geological smvey now being carried on in Great Biitain, where, unlike this Colony, every facility exists for examining the country, and accurately recording all obseI:vations made in the field, on the minutely accurate one inch maps of the Ordnance Survey. . , (Signed) ALFRED R. C. SELWYN, Geological Surveyor. Dy Authority: JORN FERRES, Government Printer, Melbourne. MAG MAG MAG MAG ))'Jl ))'Jl Sli Sli WARABUL WARABUL fUT fUT / / • • 241iU 241iU "AN "AN MAG MAG y y ' ' COR COR . . r 20"5 20"5 MAG y and and E. E. f.S."S f.S."S N~l N~l . . ' A n n a a c c Porph Set:tio 1 1 • • G< G< M M MA .lava, .lava, pt:bMa pt:bMa f1T'«i'iV f1T'«i'iV 20"JY 20"JY roUiiUII roUiiUII fV fV Qumtz Qumtz Plenty- r r a a my my Hcrrizontal Hcrrizontal · r r G~ G~ v v ve MA Ri fuRLONCS fuRLONCS a a S. S. ~tvc ~tvc • • " " black black 1 1 & Ields]Jai Ields]Jai .1:.}5" .1:.}5" c c SeAL£ SeAL£ as as n n lJ lJ th. th. u u e l l Co Co .b .b wi ': ': e-nv e-nv . . t t rec Sept.tl8Sfi Sept.tl8Sfi ky .RcceJtt .RcceJtt nark nark ,_ ,_ • • • • Melboum.t: ' ' loop Offza. Offza. Om.erals Om.erals a a a a e e e e SIUVI!JW SIUVI!JW 108 108 :forest- ck ck c c RANm;s. RANm;s. " " X . a a v at at a a A A . 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