A factory-owner， hearing what depth I had found， thought that it could not be true， for， judging from his acquaintance with dams，sand would not lie at so steep an angle.  But the deepest ponds are not so deep in proportion to their area as most suppose， and， if drained， would not leave very remarkable valleys.  They are not like cups between the hills； for this one， which is so unusually deep for its area， appears in a vertical section through its centre not deeper than a shallow plate.  Most ponds， emptied， would leave a meadow no more hollow than we frequently see.  William Gilpin， who is so admirable in all that relates to landscapes， and usually so correct， standing at the head of Loch Fyne， in Scotland， which he describes as "a bay of salt water， sixty or seventy fathoms deep，four miles in breadth，" and about fifty miles long， surrounded by mountains， observes， "If we could have seen it immediately after the diluvian crash， or whatever convulsion of nature occasioned it，before the waters gushed in， what a horrid chasm must it have appeared！

　　"So high as heaved the tumid hills， so low Down sunk a hollow bottom broad and deep，Capacious bed of waters."

　　But if， using the shortest diameter of Loch Fyne， we apply these proportions to Walden， which， as we have seen， appears already in a vertical section only like a shallow plate， it will appear four times as shallow.  So much for the increased horrors of the chasm of Loch Fyne when emptied.  No doubt many a smiling valley with its stretching cornfields occupies exactly such a "horrid chasm，" from which the waters have receded， though it requires the insight and the far sight of the geologist to convince the unsuspecting inhabitants of this fact.  Often an inquisitive eye may detect the shores of a primitive lake in the low horizon hills， and no subsequent elevation of the plain have been necessary to conceal their history.  But it is easiest， as they who work on the highways know， to find the hollows by the puddles after a shower.  The amount of it is， the imagination give it the least license， dives deeper and soars higher than Nature goes.  So， probably， the depth of the ocean will be found to be very inconsiderable compared with its breadth.

　　As I sounded through the ice I could determine the shape of the bottom with greater accuracy than is possible in surveying harbors which do not freeze over， and I was surprised at its general regularity.  In the deepest part there are several acres more level than almost any field which is exposed to the sun， wind， and plow. In one instance， on a line arbitrarily chosen， the depth did not vary more than one foot in thirty rods； and generally， near the middle， I could calculate the variation for each one hundred feet in any direction beforehand within three or four inches.  Some are accustomed to speak of deep and dangerous holes even in quiet sandy ponds like this， but the effect of water under these circumstances is to level all inequalities.  The regularity of the bottom and its conformity to the shores and the range of the neighboring hills were so perfect that a distant promontory betrayed itself in the soundings quite across the pond， and its direction could be determined by observing the opposite shore.  Cape becomes bar， and plain shoal， and valley and gorge deep water and channel.

　　When I had mapped the pond by the scale of ten rods to an inch，and put down the soundings， more than a hundred in all， I observed this remarkable coincidence.  Having noticed that the number indicating the greatest depth was apparently in the centre of the map， I laid a rule on the map lengthwise， and then breadthwise， and found， to my surprise， that the line of greatest length intersected the line of greatest breadth exactly at the point of greatest depth，notwithstanding that the middle is so nearly level， the outline of the pond far from regular， and the extreme length and breadth were got by measuring into the coves； and I said to myself， Who knows but this hint would conduct to the deepest part of the ocean as well as of a pond or puddle？  Is not this the rule also for the height of mountains， regarded as the opposite of valleys？  We know that a hill is not highest at its narrowest part.

　　Of five coves， three， or all which had been sounded， were observed to have a bar quite across their mouths and deeper water within， so that the bay tended to be an expansion of water within the land not only horizontally but vertically， and to form a basin or independent pond， the direction of the two capes showing the course of the bar.  Every harbor on the sea-coast， also， has its bar at its entrance.  In proportion as the mouth of the cove was wider compared with its length， the water over the bar was deeper compared with that in the basin.  Given， then， the length and breadth of the cove， and the character of the surrounding shore， and you have almost elements enough to make out a formula for all cases.

　　In order to see how nearly I could guess， with this experience，at the deepest point in a pond， by observing the outlines of a surface and the character of its shores alone， I made a plan of White Pond， which contains about forty-one acres， and， like this，has no island in it， nor any visible inlet or outlet； and as the line of greatest breadth fell very near the line of least breadth，where two opposite capes approached each other and two opposite bays receded， I ventured to mark a point a short distance from the latter line， but still on the line of greatest length， as the deepest.  The deepest part was found to be within one hundred feet of this， still farther in the direction to which I had inclined， and was only one foot deeper， namely， sixty feet.  Of course， a stream running through， or an island in the pond， would make the problem much more complicated.

　　一個工廠主，聽說了我所發現的深度之后，認為這不是真實的，因為根據他熟悉水閘的情況而言，細沙不能夠躺在這樣峻削的角度上。可是最深的湖，按它的面積的比例來看，也就不像大多數人想象的那么深了，如果抽干了它的水來看一看，留下的并不是一個十分深透的山谷。它們不是像山谷似的杯形，因為這一個湖，就它的面積來說已經深得出奇了，通過中心的縱切面卻只是像一只淺盤子那樣深。大部分湖沼抽干了水，剩下來的是一片草地，并不比我們時常看到的低洼。威廉。吉爾平在描寫風景時真是出色，而且總是很準確的，站在蘇格蘭的費因湖灣的尖端上，他描寫道，“這一灣鹽水，六七十英尋深，四英里闊，”約五十英里長，四面全是高山，他還加以評論：“如果我們能在洪水泛濫，或者無論大自然的什么痙攣造成它的時候，在那水流奔湍人內以前，這一定是何等可怕的缺口啊！”“高聳的山峰升得這高，低洼的湖底沉得這低，闊而廣，好河床――。”可是，如果我們把費因湖灣的最短一條直徑的比例應用在瓦爾登上，后者我們已經知道，縱切面只不過是一只淺盤形，那末，它比瓦爾登還淺了四倍。要是費因湖灣的水一古腦兒倒出來，那缺口的夸大了的可怕程度就是這樣。無疑問的，許多伸展著玉米田的笑瞇瞇的山谷，都是急流退去以后露出的“可怕的缺口”，雖然必須有地質學家的洞察力與遠見才能使那些始料所未及的居民們相信這個事實。在低低的地平線上的小山中，有鑒識力的眼睛可以看出一個原始的湖沼來，平原沒有必要在以后升高，來掩蓋它的歷史。但是像在公路上做過工的人一樣，都很容易知道，大雨以后，看看泥水潭就可以知道哪里是洼地。這意思就是說，想象力，要允許它稍稍放縱一下，就要比自然界潛下得更低，升起得更高。所以，海洋的深度，要是和它的面積一比，也許是淺得不足道也。

　　我已經在冰上測量了湖的深度，現在我可以決定湖底的形態了，這比起測量沒有凍冰的港灣來要準確得多，結果我發現它總的說來是規則的，感到吃驚。在最深的部分，有數英畝地是平坦的，幾乎不下于任何陽光下、和風中那些被耕植了的田野。有一處，我任意地挑了一條線，測量了三十桿，可是深淺的變化不過一英尺；一般他說來，在靠近湖心的地方，向任何方向移動，每一百英尺的變化，我預先就可以知道，不過是三四英寸上下的深淺。有人慣于說，甚至在這樣平靜的、沙底的湖中有著深而危險的窟窿，可是若有這種情況，湖水早把湖底的不平一律夷為平底了。湖底的規則性，它和湖岸以及鄰近山脈的一致性，都是這樣地完美，遠處的一個湖灣，從湖的對面都可以測量出來，觀察一下它的對岸，已可以知道它的方向。岬角成了沙洲和淺灘，溪谷和山峽成了深水與湖峽。

　　當我以十桿比一英寸的比例畫了湖的圖樣，在一百多處記下了它們的深度，我更發現了這驚人的一致性了。發現那記錄著最大深度的地方恰恰在湖心，我用一根直尺放在最長的距離上畫了一道線，又放在最寬闊的地方畫了一道線，真使人暗暗吃驚，最深處正巧在兩線的交點，雖然湖的中心相當平坦，湖的輪廓卻不很規則，而長闊的懸殊是從凹處量出來的，我對我自己說道，誰知道是否這暗示了海洋最深處的情形之正如一個湖和一個泥水潭的情形一樣呢？這一個規律是否也適用于高山，把高山與山谷看作是相對的？我們知道一個山的最狹的地方并不一定是它的最高處。

　　五個凹處中有三個，我全去測量過，口上有一個沙洲，里面卻是深水，可是那沙洲的目的，不僅是為了面積上擴張，也為了向深處擴張，形成一個獨立的湖沼似的盆地，而兩個岬角正表明了沙洲的方位。海岸上的每一個港埠的入口處也都有一個沙洲。正如凹處的口上，闊度大于它的長度，沙洲上的水，在同比例度內，比盆地的水更深。所以把凹處的長闊數和周遭的湖岸的情形告訴給你之后，你就幾乎有充分的材料，可以列出公式，凡是這一類情況都用得上它。

　　我用這些經驗來測量湖的最深處，就憑著觀察它的平面輪廓和它的湖岸的特性，為了看看我測量的準確程度如何，我畫出了一張自湖的平面圖，白湖幅員占四十一英畝左右，同這個湖一樣，其中沒有島，也沒有出入口：因為最闊的一道線和最狹的一道線相當接近，就在那兒，兩個隔岸相望的岬角在彼此接近，而兩個相對的沙洲彼此遠距，我就在最狹的線上挑了一個點，卻依然交叉在最長的一條線上的，作為那里是最深處。最深處果然離這一個點不到一百英尺，在我定的那個方向再過去一些的地方，比我預測的深一英尺，也就是說，六十英尺深。自然，要是有泉水流入，或者湖中有一個島嶼的話，問題就比較復雜了。

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