THE WAIKATO GRAVEL DEPOSIT.

Waikato Times, Volume XXXIII, Issue 2683, 21 September 1889, Page 2 (Supplement)

THE WAIKATO GRAVEL DEPOSIT.

Tim following is a report of a lecture on the above subject delivered by Mr H. R, Hyatt in tho Wesh-yau Schoolroom, Cambridge, on Friday evening, September 6i.li.

iNTiioiitrrrrotf.—Much has been said and written on tho subject of "Science and Revelation." We live in an ago of energei.iii and trenchant enquiry, which is not si wad by tho holiest thing of Religion ii"r by the most intricate working* of Nature. But tha tune is now past when Religion quaked at each discovery of Science. Religion now gratefully ao knowledges Science as her handmaid, while Science rejoices to decorato true Religion with her fairest flowers, and to support her claims upon tho hearts and mind of man. As Religion is a revelation of spiritual things, so is Scieure a rovelat'.on of natural things. Both reveal to man facts that he could not otherwise have known. What is Geology but a divinely written unerring account of the past stages of the earth's history ?—for so wonderful are tho works of God that every deed records itself, and the mighty mountains, tho everl.isting rocks, tho thuuder-riceu precipices are but the different books of Nature's Bible, stored with inexhaustible supplies of knowledge for all who have eyes to sec, and ears to hoar. Tho simplest mind can gain much from them if observant, while to tho more enlightened eye of the Geologist thoro open such unending vistas of Truth and Goodness as will provide material for endless development. Tho eye of the poet, often precedes in a mystical fashiou the discoveries of Science. Song before the Science of Geology was ever thought of, the immortal bard found

J.'on£ues in tree, books in running brooks. Sermons in stones, and good in everything

Let us look upou Geology thereford as the Creator's revelation of bis mighty worke, when thero were as yet no human eyes to gaze upon them ; and in this spirit I will ask your attention for a short time while I endeavour to iuterpret to you as simply as possible, a few pages from the big book of prravel which underlies our little town of Cambridge.

Lack ok Observation'.—lt is to be regretted that so many people make so little uso of their eyes, I often hear my friends say that there is nothing to see about hero ; but did they over look for anything ? lam afraid ri">t ; and to snch'T would say " Seek aud ye shall find." I shall never forget, the day—nearly niue years ago—when I first stood at tho foot of Pukekura Hill sind looked upon the regular and strongly defined terraces, ntrctched out before mo one above the other, on either side of the river ; I remember standing thero like a seer in a trance, until I had satisfied my mind as to their cause.

Waikato Plain*.—lf you stand upon any of the hills around and look down upon tho wide level plain stretched out before you, with the hills rising abruptly from its edge, the first idea it would impress upon jour mind would bo that of an extensive lake with its unbroken surface suddenly petrified and covered with verdure. Upon 11 closer examination we find that it really was a lake at one time, having an outlet probably into the Piako or Thames River, Let me take you in thought to the shores of some lake and let us observe what is going on. Iu the Swiss lakes, for example, wo invariably find a dark muddy torrent entering the lake at ono end, w bile from the other end issues a clean crystal stream which carries the surplus waters to the sea. Why this change 1 If we think for a moment it may occur to us that the current of the stream carries the sand and mud silong with it aud thus renders the stream muddy, while in the lake tho water has little or no motion aud thus allows its sand and mud to settle upon the bottom in tho form of sediment. On slackening its speed thestreim deposits first its heavier gravel, next its sand and lastly its fine mud. Thus we may expect tho sediment at tho bottom to bo arranged in layei-H, or, as wo say, in strata. Now let us visit ono of the gravel pita in our own neighbourhood : —on every side we behold tho layers or strata, thus proviusr tho water-origin, of tho gravel. We therefore come to the conclutiou that tho Waikato plain was originally an extensive lake that has beou gradually silted up with tho deposit of gravel washed down by its affluent Streams. Such vro call an alluvial plain. How long a time tho silting up has occupied would be difficult to say, and it would require a more experienced person than myself to proffer ever an approximate idea.'

PKBisr.Ks.-Each little pebble has its own individual story to tell. By their rounded water-worn surface we gather tbat; they have been rolled along together and carried some distance by the streams ere they were deposited upon the floor of the lake. But they have much more than this to tell us had we to listen to their separate histories.

Ancient Forest.—Hitlierto we have been examining only the surface of onr gravel plain. We will now go down lower. We need not dig a deep pit right down to the bottom of the gravel, for that has been done for us already in many of the gullies, and in the bed of the river itself. On the Gorton Koad about a mile from Cambridge there is a very interesting gully which lias a great store of geological history to tell us. Its geological value is owing to the fact that it n at this present time in proces3 of being washed out by every heavy fall of rain ; and as each mass of gravel is washed away it leaves the place pretty much the same as it was before the gravel was deposited there. Those who hove not visited it have an intellectual treat in store. Let me take your thoughts there for a moment. Your attention is at once attracted by the number of tree stumps all in good state of preservation and in the upright position in which they have grown, with their roots still fixed in their ancient sail. These trees are the same as t'roH' in our bushes now. Kahekatea, P-iriri, Puketea, Punga, and many others all quite recognizable. And this is. not an isolated example. Other gullies and the bed of the river it3elf show the same upright tree stumps though perhaps in les3 perfect form. What conclusion are we to come to ? It is quite clear that these trees could not have grown at the bottom of the lake. How are we to account for their presence. It is evident that these trees must have i/roivn before the lake existed. U 7 e find then that the district in which we live lias hid as it were three distinct existences, (1) as a forest covered country, (2) as a lake, (3) as an alluvial plain. The extent of history we have traced luck is but a very *mall fragment of the vast geological ages which can be traced in the rocky crust of the globe. To speak scientifically we have only been examiniug recent formations and changes ; but I think we have gone over sufficient ground for one evening's study, and we will now put together the facts we have been reviewing and trace therein the past history of the three latter stages of geological development of the Waikato Plains.

(1) FoRKi-T. —We have found that there was once a forest covered plain at a lower level by about 100 feet than the one which we at present see around us. Though wo cannot form any correct idea as to how long ago this was, it must at least have been some thousands of years ago, as will appear from what we shall notice as we proceed.

(•2) JjAKK.—How this forest became a lake I am not in a position to say. It may have been caused by a subsidence of the land before the volcanic action in the neighboring hills had become quite dormant. When we take into consideration the comparative thinness of the earth's crust, such a subsidence is nothing extrrordinary. In fact the traces of upheav; 1 and depression of paits of the earth's surface, repeated time after time, So'"e--times in succession, sometimes alternately, are everywhere met with in all rock formations. It is also possible that this lake may have been formed by the upheaval of the land lower down the river. However, it became a lake of fresh water. We know that it was not a branch of the

sea because if it were so we should find tho remains of shells and sea-animals mingled with the gravel ; but such is not the c,»sp, so we may safely infer that it was a fresh water lake, and I believe that this lake still lives in the traditions of the Maoris.

Dki-osit. —The first sediments which were carried down into this lake consisted chiefly of light pumice sand and cravel. We discover this from the fact that all the lower strati are of pumice sand and gravel and this is tl)2 reason why the lower terraces on the sides of the river have such poor and unproductive soil. Tho pumice being so light was evidently washed into the lake first, and afterwards the heavier sand and gravel. The upper strata coutain very little mimice, if any, being almost entirely formed of gravel, silicious sand, and fragmentary quartz crystals. In the lower strata a quantity of carbonized wood or charcoal is to be found being the fragmentary remains of the trees referred to. Thus as time went on thick layers of gravel and sand were piled upon the floor of this lake until the lake became quits shallow, and then another change came about. It is probable that the waters of the lake burst through the hills a little below Ngaruawahia and formed what is now the Taupiri Gorge. This would have tho effect of draining the lake and leaving tho gravel deposits dry in the form of an alluvial plain.

Waikato Swamps.—When a river periodically overflows its banks and floods the adjoining plains most of its sediment is deposited near its banks, and the plain becomes higher near the rirer than it is farther away. This is the case with the Waikato plain, ami we find that the lower parts of the plain at a distance from the river have been eonverted into swamps. It has been found that the gravel underlies these swamps, and in some cases, where the swamp drains h»ve been dug down to the gravel, the flow of water has quickly washed them out into large gullies.

Tbrbaces.—The river terraces that are so noticeable are simplv the different beds that the river has successively formed for itself. They arc found on many rivers, especially those flowing through light gravelly formations. The power of moving water is enormous. The recent calamity in America which swept away whole towns is a very forcible illustration of this. I also remember some years ago at I'aeroa several million tons of gravel were washed out of a drain by heavy rains in a single night. The pile of detritus thus formed is now used, I believe, as a road.

Tho Waikato river when it first flowed over this newly formed plain was a wide, shallow, sluggish stream ana , has left traco3 of its original banks near the National Hotel Cambridge and at the hotel at Cambridge West, a width of about half a mile. Iu a wide, shallow stream the current would be more marked in one part of its bed than others ; this part would gradually get worn down until it was deep enough to contain the whole stream, and then the remainiusr portions of its former bed would he left dry, except perhaps, in times of flood. Thus from time to time the Wakato river has worn for itself deeper, and narrower channels ono within the other, each time leaving parts of its former bed dry, in the form of a terrace on either side. Sometimes after a flood it has slightly changed its bed and formed for itself a new channel. This U particularly noticeable on the Gorton Road just beyond tho bridge. This road evidently passes along an old forsaken bed of the river, which has shifted its course in a tirna of flood It may seem strange but it is nevertheless true that when we are walking upon any of these terraces, we aro walking upon what was at ono time the bottom of tho river. The Waikato is still lowering its bod a« may bo remarked from the appeal ance of those large rocks just below tho bridge at Cambridge. Eight yesirs ago those roe.ks were constantly covered with water except in times of drought ; now they are always dry, and as there is no reason for believitig that the qnantity of water has diminished, wo are forced to conclude that the bod has been deepened.

CilAxiiu.—Thus the most forcible lesson that geology has to teach us is that we live in a world of change. Says the Poet Laureate-

There rolls tbo deep where grew the tree. O earth, what changes thou hast seen ' There, where the long street roars, hath been The stillness of [lie central sea.

The hills are shadows, and they flow From form to form, and nothing stands ; They melt like mist, the solid lands,

Like clouds they shape themselves and go

Whenever we turn our eyes wo find that this is a world of change, of decay and re-formation ; and as nueli is it not a fit dwelling place for mortal beings who are too apt to change, to decay and fall away from the Truth, but who, like the wasted material in our lakes and rivers, are still capable of re-formation into]verdant vinoyards and fruitful soil, bringing forth fruit some thirty fold, some sixty and some an hundred. A kind word or a noble thought is never lost. Like the sediment on the floor of some lake, though lost sight of, and forgotten, they will one day reappear in the flowers of some alluvial soil. Change within us and change around us ! When we fully realize thin, is it not a privilege and a boon to bo able to turn our thoughts to Him who is " tho same yesterday, to-day, and for ever" and to bo able to say from our hearts— Chinee and decay in all around I sec , O Thou who chaiigest nut. abide with me !