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-THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[OOTOBBR, 



extensive tracts of country, and large earthworks, geology is most 

 e<^sential as a guide. Tlie selection of the line of country, the choice 

 of materials, the nature of substrata to be mined and cut tlirougli, the 

 springs likely to be met with require geological skill to produce a 

 good and safe plan, and the same knowledge is requisite in conduct- 

 ine subsequent operations, both for the engineer and contractor. Much 

 of the waste of capital and subsequent litigation and in case of Ranger s 

 contracts on the Great Western Railway was caused by want ot know- 

 ledge as to the position of the Pennant stone and its probable hard- 

 ness. Professor Ansted observes : — 



In the case of a railroad, more than ordinary care and attention is often 

 required to enable the engineer to decide how far he may safely, and with 

 justice to his employers, contemplate the overcoming of natural dilhcultiesin 

 a country to he passed over, in order to escape from other ditnculties of a 

 different kind, arising from the local value of property, and the arrangements 

 that have to he made with landowners. In this respect, an acquaintance 

 with the principles of Geology cannot fail to he exceedingly useful, as sug- 

 gesting resources, the existence of which could not otherwise he guessed at, 

 or, at least, which could not be discovered without a minute local knowledge 

 of the district. For, let us suppose two engineers, the one unacquainted 

 with the order of superposition of the strata, and ignorant even of the fact 

 of stratification at all, in its Geological sense, and the other a practical and 

 well-informed student of Geology. And let us assume these two men to he 

 required to construct a line of railroad from London to Dover. The mere 

 engineer, having no knowledge of Geology, would only he aware, in a general 

 wiiv.that between London and the Weald of Kent, there was a range of 

 chalk hills, (the North Downs,) but that afterwards the country was tolerably 

 level, as far to the east as Folkstone. lie would soon find that, with the 

 exception of the Dart and the Mole, two rivers running into the Thames, the 

 one at Dartford in Kent, and the other near Kingston in Surrey, there was 

 no complete drainage across the hills, and therefore no continuous valley 

 leading to the level country, and these two valleys would both be found ill 

 adapted for the object in view. On further examination, partial valleys 

 would, however, he discovered, and one of these, we may suppose, would he 

 selected as the most convenient. The rest of the work to Folkstone would 

 he calculated for as work of the ordinary kind, and cuttings and embank- 

 ments would be made without any reference to the peculiar circumstances of 

 the strata. Let us now see what would be the inquiries and conclusions of 

 the Geological engineer under similar circumstances. The line of road by 

 Croydon is sufficiently marked out by the physical geography of the district, 

 and need not be again referred to. Our engineer, however, having settled 

 these preliminaries, would consider that in the course of his work he must 

 cut through a considerable portion of the lower part of the London Clay, 

 which he would know beforehand to consist of sand and gravelly matter, mixed 

 with some tenacious clay, and that he would then have to tunnel througli 

 the chalk, coming out upon the lower beds, which on examination he would 

 find were considerably tdted towards the north. His hne would thus c.ury 

 him along the direction of a small disturbance transverse to that which had 

 originally elevated the beds of chalk. Through part of this he would have 

 to tunnel, and he would be aware that in a district like that extending along 

 the line of the chalk hills there was little danger ot meeting with hard beds, 

 or with intruded igneous rock. The advantage of being thus able to predi- 

 cate with considerable certainty as to the nature of the ground througli 

 which the road was to be cut, must be evident to every practical man, and 

 we shall soon perceive how far such knowledge is immediately applicable. 

 Besides this acquaintance with the condition of the chalk the Geological en- 

 gineer in this case would remember that his cuttings and embankments 

 would have to be made for the most part at right angles to the strike of the 

 beds, but that in some cases the London Clay, having a different local dip, 

 would be cut in a slant direction. Lastly, he would be awaie that when he 

 had crossed the chalk, and the other beds of the cretaceous group, he would 

 come upon the Weald Clay, a bed dipping northwards, and which he would 

 have to traverse in a westerly direction, and therefore directly on the line of 

 strike. Now the beds of the London basin, consisting, as they generally do, 

 of clay alternating with occasional sands, are exceedingly dangerous when 

 deep cuttings or tunnels are made through them, which are not properly de- 

 fended. And this is the case, because the rain, washing through and carry- 

 ing away the sands where a section has been made, leaves the upper bed of 

 clay barely balanced upon the lower, and with a slippery surface between 

 them. The inevitable consequence of such a condition of things is, that 

 after a short time the upper bed shps quietly down in the direction of its 

 dip, falling upon and filhng up the cutting that has been made through it. 

 Accidents of this kind have happened too frequently not to be familiar to 

 every engineer, and the cause is now to a certain extent generally under- 

 stood ; but nothing short of a knowledge of the structure of the country, or, 

 in other words, of the principles of Geology, will enable any one effectually 

 to avoid this danger, because it is one constantly recurring, and requiring 

 different management, to a certain extent, for each individual case. The 

 Geological engineer will know his danger, and will endeavour to provide 

 against it beforehand. The mere empiricist who l<nows only the rule 

 of practice on the occasion, will, perhaps, bring out at last the same, or 

 nearly the same, result ; hut it will be by that most expensive and least cre- 

 ditable of all methods, a succession of failures.— It would be interesting and 

 exceedingly instructive to consider, with respect to their bearing upon Geo- 

 'ogy, several of the great lines of rail-road in England and elsewhere. It 



would be found that all of them, without exception, have reference at least 

 as much to the Geological as to the Geographical structure of the country, 

 and that in each, the great works in cutting and tunnelling, if they were 

 not originally constructed on those principle advocated in the text, have been 

 since altered, or must shortly be altered, in consequence, or in certain antici- 

 pation, of accidents. By in the outline of the subject at present offered, such 

 a detail would be clearly out of place. , . , u 



Tills will serve to illustrate the course of investigation which the 

 scientihc engineer is bound to pursue who duly regards his own repu- 

 tation and the interests of his employers. The treatment ot slips, a 

 difficulty with which railway working has made us acquainted is more 

 geological than engineering, and as it is a subject which "eeplv in- 

 terests professional men, and on which all experience is valuable, we 

 shall bring before them Professor Ansted's observations. He says— 



The only defences, indeed, in these cases seem to be, (1) Thorough surface 

 drainage on the line of outcrop of each bed cut through ; (2) A greater slope 

 on the rise side of the bed than is necessary on the other or dip side ; and 

 (.3), Careful attention from time to time to see that no tendency to a slip 

 shows itself. The methods to be pursued with regard to clay cuttings, and 

 the accidents that are incidental to them, belong as much to cuttings for or- 

 dinary roads and canals as raihoads, and are applicable in many cases, when 

 other beds than clay (such as courses of limestone) are separatad by partings, 

 which on exposure to the atmosphere, or on suffering the drainage of water 

 through them, become slippery, and cause the upper and lower beds to lose 

 their coherence. Even in an embankment, if the successive layers of earth 

 are not level, an accident not unfrequently happens from the same cause, the 

 moisture penetrating the beds, and if not loosening them under ordinary cir- 

 cumstances of temperature, affecting them afterwards during severe frost, 

 when the expansion of the freezing water produces effects that can hardly be 

 calculated, until they are unhappily seen and felt. The advantage derived 

 from a knowledge of Geology in engineering consists (it will now be nnaer- 

 stood) in teaching the engineer how to avoid danger, or if he must be ex- 

 posed to it, how to provide a remedy from the beginning. It often happens 

 that a teudeiicv once produced in the beds to slip, cannot afterwards be 

 stopped, although the first step towards the mischief might have been pre- 

 vented by timely application of preventive measures. The slope, in such 

 dangerous cuttings, should have some, and often a considerable reference to 

 the dip of the bed, for however it may seem that the rain and other atmos- 

 pheric agents must wash away the loose sand equally on both sides of the 

 road, this is by no means the case in reality, and the washing will be far 

 more rapid, and the tendency to slip down in large masses incomparably 

 greater on the one side than on the other. On the one side, therefore, of 

 such a cutting the judicious planting of grass will often be a sufficient defence 

 even with a steep slope, while on the other, even a stout wall will be in snf- 

 ficient to prevent a slip from the very first day of exposure.— The direction 

 and the degree of exposure of the face of the cutting in such cases wdl also 

 be important subjects of consideration. In our own country a south-west 

 * exposure is in most cases far more likely to be affected by atmospheric causes 

 than any other ; but this is not invariably the case, and may by local in- 

 fluences be less liable to be injured than any other.— There are, indeed, very 

 few cases in which the considerations of geological structure and relative ex- 

 posure ought not so to modify the calculations of the eugmeer as to induce 

 him to make a greater slope on one side than on the other of every deep 

 cutting. 



Another department of engineering belongs decidedly to geology, 

 the construction and improvement of harbours, and he must be a bung- 

 ling practioner, who does not make himself well acquainted with the 

 natural laws influencing the coast to be acted upon, and ihe operations 

 of the sea upon it. One who goes to work without such knowledge 

 and such care, too generally brings forth sliingletraps as the result ot 

 his labours, and wastes the money of his employers in vain attempts 

 to baffle nature, instead of bringing her operations to his aid. We 

 have too often expressed ourselves as to the unsound, unsatisfactory and 

 unscientific state of harbour engineering in the present day, to make 

 further remarks in reference to it now. 



In any kind of building operations, the engineer and architect will 

 profit by bis geological knowledge, he will take care not to erect an 

 establishment where the strata maybe liable to slip down, he will 

 look well to his foundation, he will find what prospects be has of ac- 

 cess to water, and what is the nature of the drainage, and before he 

 proceeds to construct his building he will carefully examine the budd- 

 ing stones, which may be available, and their relative durability, 

 cheapness, colour and weight. As this subject is howevernow fami- 

 liar to our readers, in consequence of the labours of the Parliamentary 

 Commissioners, and the lectures of Mr. G. F. Richardson, we shall 

 not dwell upon it longer. 



We have already made some allusion to wellsinking, but belore we 

 dismiss it altogether we must make some few more remarks, as it is a 

 subject daily becoming of more importance. The enquiries of Govern- 

 ment and the Legislature into the state of towns have not only opened 

 the way for extensive operations by the engineer in drainage and 

 sewage, but they have established also the deficient supply o','***" 

 to large populations. This is a want which must be remedied mw 



