CHAPTER II. LACUSTRINE AND FLUVIATILE BRICK-EARTHS.

 The great variability of brick-earths deposited in river valleys is reflected to some extent in those laid down in lakes, though the size of the latter is frequently a controlling factor. The chief difference consists in the broader expanse of the sediment¹ laid down—especially in large lakes—and variation in structure is not so noticeable horizontally. Let us consider a simple case in which a lake is fed by a large river bringing down abundant sediment. The lake acts as a species of settling tank, and the method of deposition² of the sediment by the river is mainly guided by the velocity³ of the stream. The tendency under normal conditions is for the river to commence parting with its sediment immediately on entering the lake. The detritus⁵ alluded⁶ to is only held in suspension by the velocity of the water; when the latter is checked, as on entering the lake, the grosser pieces subside⁷, and as its rapidity becomes progressively curbed⁸, medium-sized fragments are compelled to give way, until at last only very minute particles are left in the water. In due time most of these also are deposited. Thus gravel⁹ is laid down before grit¹⁰, grit before sand, and sand before clay.

If the velocity of the river always remained the same, we should be presented with thick accumulations of the same character in sharply defined areas. But it is always changing. With every storm and every steady18 rain the motion of the river becomes greatly accelerated, with the result that the deposits for the time being are deposited farther out in the lake than in more quiescent¹¹ periods. In this way we may have a gravel thrown down on sand, sand on clay, and so on.

From the foregoing observations it will be gleaned¹² that, in general, deposits in large lakes are more persistent¹³ in character than are river deposits; indeed, in very large sheets of water, as Lake Superior, Lake Erie, &c., they are in this sense more comparable with sediment of marine¹⁴ origin.

The practical value of this knowledge hinges on the correct determination of the origin of the deposits, and it is not always easy to identify a brick-earth of lacustrine origin. In all probability the tyro¹⁵, on meeting one, would be disposed to regard it as a river deposit pure and simple. The valuation of a brick-earth property under such circumstances would thus be greatly in favour of the prospective¹⁶ purchaser; but it would be disastrous¹⁷ for the seller. A random¹⁸ section, except in the case of a very large lake, would show gravels¹⁹, sands and clays in much the same manner as the river deposits described in the last article of this series. But, as previously²⁰ remarked, on the whole they would be more continuous and persistent, and what is quite as important, the mineral composition of each stratum²¹ would be equally homogeneous when traced over wide areas. The geologist²² distinguishes a lacustrine deposit from one of fluviatile origin more from its mineral constitution and the general disposition²³ of the beds, as ascertained²⁴ by mapping, than from evidence afforded by fossils—these latter for the most part being similar to those found in the deposits left by rivers.

The well-known brick-earth called “Reading mottled19 clay,” so extensively developed on the outskirts²⁵ of the London basin, and in the Isle²⁶ of Wight and Hampshire generally, furnishes a good example of a lacustrine deposit. Many millions of bricks are made from this bed every year, and in some parts of the districts mentioned the stratum is thick and extensively developed. It is pure enough to be suitable for terra-cotta manufacture here and there. No one who had seen this remarkable²⁷ deposit could possibly fail to recognise it again. The natural colour of the clay when damp is brilliant red, scarlet²⁸ or crimson²⁹, in large blotches³⁰ and patches mottled tea-green and yellow, and locally white.

We have been intensely amused to note the efforts in recent years to obtain possession of a few acres of this coveted³¹ deposit for brickmaking in divers³² localities. Not long since we visited a large brickmaking establishment where these Reading plastic clays are actively³³ raised and used, the works being situated³⁴ four miles from the nearest railway. There were no other brickworks between it and the railway line, and there was no water accommodation. Enquiry revealed the fact that the greater part of the intervening land belonged to the same landowner as the ground where the brickyard stands, and that no difficulty was apprehended³⁵ of the owner letting out such intervening land for the same uses and on the same terms if other brickyards were contemplated³⁶. The proprietor³⁷ of the brickyard in question volunteered the information that the reason he started so far from the railway was because the earth at the point selected was the only kind suitable for brickmaking in the neighbourhood. We then questioned him as to his knowledge of the brick-earths in the district, and eventually elicited³⁸ the fact that he chanced upon the spot selected, without any reasoning therefor,20 and commenced operations. As a matter of fact, precisely³⁹ the same clay extended from his works all the way to the railway line, and had he known anything whatever of the geology of the district (even the merest boy’s knowledge of the subject), he would have seen how to save that four miles of road carriage. What prevented him from knowing the fact was a thin mantle⁴⁰ of gravel and soil about four feet in thickness, which covered the plastic clay in the area generally, except in the immediate⁴ vicinity of his brickyard. That was in reference to a lacustrine deposit—the Reading plastic clay—and shows the value of knowing something of its persistent character; if it had been a river deposit there would not have been so much room for wonderment.

To give some idea of the extent of that particular horizon, we may say that not only is the plastic clay alluded to found so extensively in the London and Hampshire basins, it is even more expanded in the north-eastern parts of France, and is there as much utilised as on this side of the Channel for brickmaking.

Lacustrine deposits are sometimes of enormous value to the clayworker, on account of the general purity of the clays. This is more particularly the case when the material deposited is in part or wholly derived⁴¹ from chemical disintegration⁴² of granitic⁴³ rocks, as in the celebrated⁴⁴ Bovey Heathfield clays near Newton Abbot, so well described in a small pamphlet by Mr. S. Smith Harvey. Here an experimental boring proved the clays to a depth of 130 feet with no signs of exhaustion⁴⁵. In the divers clay-pits but a small proportion of waste is found, the different levels vary in composition, and, like almost all thick clays, improve in quality as the depth increases. The strata⁴⁶ are very irregular towards the surface, due perhaps to the action of local21 freshets in the final periods of the history of the lake. These clays are extensively employed for the manufacture of stoneware pipes, facing and other bricks, fire-bricks, etc. They constitute a somewhat remarkable exception to the class of clays laid down in lakes, as a rule, and, as will have been observed, are of enormous thickness.

We have very little to say in regard to estuarine⁴⁷ brick-earths; as might readily be anticipated, they are intermediate in character between fluviatile and marine deposits, and approach the one or the other according to position in the estuary⁴⁸. On the whole, they are variable in character, individual beds being thin. The strata frequently contain abundant plant remains⁴⁹ (pieces of wood, etc.), and, except in the case of large rivers, are not noted⁵⁰ for yielding very good brick-earths. Sometimes, however, the quality of the clays is not bad, as instance the bricks made in Lincolnshire and Northamptonshire from Jurassic Estuarine clays.

1 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

2 deposition   

n.免职，罢官；作证；沉淀；沉淀物

参考例句：

• It was this issue which led to the deposition of the king.正是这件事导致了国王被废黜。
• This leads to calcium deposition in the blood-vessels.这导致钙在血管中沉积。

3 velocity   

n.速度，速率

参考例句：

• Einstein's theory links energy with mass and velocity of light.爱因斯坦的理论把能量同质量和光速联系起来。
• The velocity of light is about 300000 kilometres per second.光速约为每秒300000公里。

4 immediate   

adj.立即的；直接的，最接近的；紧靠的

参考例句：

• His immediate neighbours felt it their duty to call.他的近邻认为他们有责任去拜访。
• We declared ourselves for the immediate convocation of the meeting.我们主张立即召开这个会议。

5 detritus   

n.碎石

参考例句：

• Detritus usually consists of gravel, sand and clay.岩屑通常是由砂砾，沙和粘土组成的。
• A channel is no sooner cut than it chokes in its own detritus.一个河道刚被切割了不久，很快又被它自己的碎屑物质所充塞。

6 alluded   

提及，暗指( allude的过去式和过去分词 )

参考例句：

• In your remarks you alluded to a certain sinister design. 在你的谈话中，你提到了某个阴谋。
• She also alluded to her rival's past marital troubles. 她还影射了对手过去的婚姻问题。

7 subside   

vi.平静，平息；下沉，塌陷，沉降

参考例句：

• The emotional reaction which results from a serious accident takes time to subside.严重事故所引起的情绪化的反应需要时间来平息。
• The controversies surrounding population growth are unlikely to subside soon.围绕着人口增长问题的争论看来不会很快平息。

8 curbed   

v.限制，克制，抑制( curb的过去式和过去分词 )

参考例句：

• Advertising aimed at children should be curbed. 针对儿童的广告应受到限制。 来自辞典例句
• Inflation needs to be curbed in Russia. 俄罗斯需要抑制通货膨胀。 来自辞典例句

9 gravel   

n.砂跞；砂砾层；结石

参考例句：

• We bought six bags of gravel for the garden path.我们购买了六袋碎石用来铺花园的小路。
• More gravel is needed to fill the hollow in the drive.需要更多的砾石来填平车道上的坑洼。

10 grit   

n.沙粒，决心，勇气；v.下定决心，咬紧牙关

参考例句：

• The soldiers showed that they had plenty of grit. 士兵们表现得很有勇气。
• I've got some grit in my shoe.我的鞋子里弄进了一些砂子。

11 quiescent   

adj.静止的，不活动的，寂静的

参考例句：

• It is unlikely that such an extremist organization will remain quiescent for long.这种过激的组织是不太可能长期沉默的。
• Great distance in either time or space has wonderful power to lull and render quiescent the human mind.时间和空间上的远距离有一种奇妙的力量，可以使人的心灵平静。

12 gleaned   

v.一点点地收集（资料、事实）( glean的过去式和过去分词 )；（收割后）拾穗

参考例句：

• These figures have been gleaned from a number of studies. 这些数据是通过多次研究收集得来的。
• A valuable lesson may be gleaned from it by those who have eyes to see. 明眼人可从中记取宝贵的教训。 来自《现代汉英综合大词典》

13 persistent   

adj.坚持不懈的，执意的；持续的

参考例句：

• Albert had a persistent headache that lasted for three days.艾伯特连续头痛了三天。
• She felt embarrassed by his persistent attentions.他不时地向她大献殷勤，使她很难为情。

14 marine   

adj.海的；海生的；航海的；海事的；n.水兵

参考例句：

• Marine creatures are those which live in the sea. 海洋生物是生存在海里的生物。
• When the war broke out,he volunteered for the Marine Corps.战争爆发时，他自愿参加了海军陆战队。

15 tyro   

n.初学者；生手

参考例句：

• She is a tyro in the art of writing poetry.她是一名诗歌创作艺术的初学者。
• I am a veritable tyro at the game.我玩这个是新手。

16 prospective   

adj.预期的，未来的，前瞻性的

参考例句：

• The story should act as a warning to other prospective buyers.这篇报道应该对其他潜在的购买者起到警示作用。
• They have all these great activities for prospective freshmen.这会举办各种各样的活动来招待未来的新人。

17 disastrous   

adj.灾难性的，造成灾害的；极坏的，很糟的

参考例句：

• The heavy rainstorm caused a disastrous flood.暴雨成灾。
• Her investment had disastrous consequences.She lost everything she owned.她的投资结果很惨，血本无归。

18 random   

adj.随机的；任意的；n.偶然的(或随便的)行动

参考例句：

• The list is arranged in a random order.名单排列不分先后。
• On random inspection the meat was found to be bad.经抽查，发现肉变质了。

19 gravels   

沙砾( gravel的名词复数 )； 砾石； 石子； 结石

参考例句：

• Suetion devices are inadequate in gravels or very porous soils. 吸水装置对砂砾或非常疏松的土壤是不适用的。
• They may form concentrated pockets in gravels. 它们可能在砾石堆积物中形成富集的矿囊。

20 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

21 stratum   

n.地层，社会阶层

参考例句：

• The coal is a coal resource that reserves in old stratum.石煤是贮藏在古老地层中的一种煤炭资源。
• How does Chinese society define the class and stratum?中国社会如何界定阶级与阶层？

22 geologist   

n.地质学家

参考例句：

• The geologist found many uncovered fossils in the valley.在那山谷里，地质学家发现了许多裸露的化石。
• He was a geologist,rated by his cronies as the best in the business.他是一位地质学家，被他的老朋友们看做是这门行当中最好的一位。

23 disposition   

n.性情，性格；意向，倾向；排列，部署

参考例句：

• He has made a good disposition of his property.他已对财产作了妥善处理。
• He has a cheerful disposition.他性情开朗。

24 ascertained   

v.弄清，确定，查明( ascertain的过去式和过去分词 )

参考例句：

• The previously unidentified objects have now been definitely ascertained as being satellites. 原来所说的不明飞行物现在已证实是卫星。 来自《简明英汉词典》
• I ascertained that she was dead. 我断定她已经死了。 来自《简明英汉词典》

25 outskirts   

n.郊外，郊区

参考例句：

• Our car broke down on the outskirts of the city.我们的汽车在市郊出了故障。
• They mostly live on the outskirts of a town.他们大多住在近郊。

26 isle   

n.小岛，岛

参考例句：

• He is from the Isle of Man in the Irish Sea.他来自爱尔兰海的马恩岛。
• The boat left for the paradise isle of Bali.小船驶向天堂一般的巴厘岛。

27 remarkable   

adj.显著的，异常的，非凡的，值得注意的

参考例句：

• She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
• These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。

28 scarlet   

n.深红色，绯红色，红衣；adj.绯红色的

参考例句：

• The scarlet leaves of the maples contrast well with the dark green of the pines.深红的枫叶和暗绿的松树形成了明显的对比。
• The glowing clouds are growing slowly pale,scarlet,bright red,and then light red.天空的霞光渐渐地淡下去了，深红的颜色变成了绯红，绯红又变为浅红。

29 crimson   

n./adj.深(绯)红色(的)；vi.脸变绯红色

参考例句：

• She went crimson with embarrassment.她羞得满脸通红。
• Maple leaves have turned crimson.枫叶已经红了。

30 blotches   

n.（皮肤上的）红斑，疹块( blotch的名词复数 )；大滴 [大片]（墨水或颜色的）污渍

参考例句：

• His skin was covered with unsightly blotches. 他的皮肤上长满了难看的疹块。 来自《简明英汉词典》
• His face was covered in red blotches, seemingly a nasty case of acne. 他满脸红斑，像是起了很严重的粉刺。 来自辞典例句

31 coveted   

adj.令人垂涎的；垂涎的，梦寐以求的v.贪求，觊觎(covet的过去分词)；垂涎；贪图

参考例句：

• He had long coveted the chance to work with a famous musician. 他一直渴望有机会与著名音乐家一起工作。
• Ther other boys coveted his new bat. 其他的男孩都想得到他的新球棒。 来自《简明英汉词典》

32 divers   

adj.不同的；种种的

参考例句：

• He chose divers of them,who were asked to accompany him.他选择他们当中的几个人，要他们和他作伴。
• Two divers work together while a standby diver remains on the surface.两名潜水员协同工作，同时有一名候补潜水员留在水面上。

33 actively   

adv.积极地，勤奋地

参考例句：

• During this period all the students were actively participating.在这节课中所有的学生都积极参加。
• We are actively intervening to settle a quarrel.我们正在积极调解争执。

34 situated   

adj.坐落在...的，处于某种境地的

参考例句：

• The village is situated at the margin of a forest.村子位于森林的边缘。
• She is awkwardly situated.她的处境困难。

35 apprehended   

逮捕，拘押( apprehend的过去式和过去分词 )； 理解

参考例句：

• She apprehended the complicated law very quickly. 她很快理解了复杂的法律。
• The police apprehended the criminal. 警察逮捕了罪犯。

36 contemplated   

adj. 预期的 动词contemplate的过去分词形式

参考例句：

• The doctor contemplated the difficult operation he had to perform. 医生仔细地考虑他所要做的棘手的手术。
• The government has contemplated reforming the entire tax system. 政府打算改革整个税收体制。

37 proprietor   

n.所有人；业主；经营者

参考例句：

• The proprietor was an old acquaintance of his.业主是他的一位旧相识。
• The proprietor of the corner grocery was a strange thing in my life.拐角杂货店店主是我生活中的一个怪物。

38 elicited   

引出，探出( elicit的过去式和过去分词 )

参考例句：

• Threats to reinstate the tax elicited jeer from the Opposition. 恢复此项征税的威胁引起了反对党的嘲笑。
• The comedian's joke elicited applause and laughter from the audience. 那位滑稽演员的笑话博得观众的掌声和笑声。

39 precisely   

adv.恰好，正好，精确地，细致地

参考例句：

• It's precisely that sort of slick sales-talk that I mistrust.我不相信的正是那种油腔滑调的推销宣传。
• The man adjusted very precisely.那个人调得很准。

40 mantle   

n.斗篷，覆罩之物，罩子；v.罩住，覆盖，脸红

参考例句：

• The earth had donned her mantle of brightest green.大地披上了苍翠欲滴的绿色斗篷。
• The mountain was covered with a mantle of snow.山上覆盖着一层雪。

41 derived   

vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取

参考例句：

• Many English words are derived from Latin and Greek. 英语很多词源出于拉丁文和希腊文。 来自《简明英汉词典》
• He derived his enthusiasm for literature from his father. 他对文学的爱好是受他父亲的影响。 来自《简明英汉词典》

42 disintegration   

n.分散，解体

参考例句：

• This defeat led to the disintegration of the empire.这次战败道致了帝国的瓦解。
• The incident has hastened the disintegration of the club.这一事件加速了该俱乐部的解体。

43 granitic   

花岗石的，由花岗岩形成的

参考例句：

• A batholith has been defined as a huge intrusive mass of granitic rock. 岩基的定义是巨大的花岗石侵入岩体。
• A granitic rock composed chiefly of quartz and mica. 一种由石英和云母构成的花岗石。

44 celebrated   

adj.有名的，声誉卓著的

参考例句：

• He was soon one of the most celebrated young painters in England.不久他就成了英格兰最负盛名的年轻画家之一。
• The celebrated violinist was mobbed by the audience.观众团团围住了这位著名的小提琴演奏家。

45 exhaustion   

n.耗尽枯竭，疲惫，筋疲力尽，竭尽，详尽无遗的论述

参考例句：

• She slept the sleep of exhaustion.她因疲劳而酣睡。
• His exhaustion was obvious when he fell asleep standing.他站着睡着了，显然是太累了。

46 strata   

n.地层（复数）；社会阶层

参考例句：

• The older strata gradually disintegrate.较老的岩层渐渐风化。
• They represent all social strata.他们代表各个社会阶层。

47 estuarine   

河口的，江口的

参考例句：

• The water above the continental shelf is moved by the tides and by estuarine currents. 潮流和河口流使大陆架上的海水流动。
• An outstanding example of the drastic alteration of the estuarine environment is found in the Netherlands. 河口湾环境发生强烈变化的一个突出的例子是荷兰。

48 estuary   

n.河口，江口

参考例句：

• We live near the Thames estuary.我们的住处靠近泰晤士河入海口。
• The ship has touched bottom.The estuary must be shallower than we thought.船搁浅了。这河口的水比我们想像的要浅。

49 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

50 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。