432 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Dkcembkr, 



structed for tlie purpose. In certain portions of tlie work the blocks have 

 been subsequently ranged from a ilivinp; bell. The buttress and the works 

 now in progress round the west end arc composed of granite masonry, dove- 

 tailed horizontally, and fixed vertically by iron lens cramps. 



Subsefjuently to the reception of the plan of Messrs. Rennie and AVhidliy, 

 most of the leading engineers of the day were consulted, under whose di- 

 rections the author has superintended the execution of the work. 



The communication is accompanied by six elaborate drawings by Mr. 

 Dobson, illustrating in detail the various stages of the work, and the mode 

 of construction. 



Mr. Rendel could have wished that the account of this interesting work, 

 the most extensive of the kind in Great Britain, bad entered more fully into 

 details, not only of the difliculties met with and overcome, but of the pecu- 

 liarities of the construction ; there were many points connected with it of 

 great importance to engineers, lie would allude to one only upon which no 

 information was given ; tlie amount of interstice in the whole cubic content 

 as compared with the mass of materials employed ; an accurfite account had 

 been kept of the quantity of stone deposited, and knowing the cube of the 

 mass at a given period, be bad ascertained the amount of interstice or vacant 

 space in the old part of the works to be at one time 37 per cent. This great 

 deficiency of solidity had arisen from the employment of an excess of large 

 stone, or rather from a deficiency of small stone to fill the interstices between 

 the large stones. 



June 22.— The President in the Chair. 

 Tlie following were elected : Joseph Colthurst, as a Graduate ; Colonel 

 George Ritso Jervis, B. E., Captain Henry Goodwyn, B. E., and William 

 Lamb Arrowsraith, as Associates. 



"On the Construction and Use of Geological Models in connexion with 

 Civil Engineeriny." By Thomas Sopwith, F. G. S., M. Inst. C. E. 



The author commences this paper with a review of the various methods 

 adopted for the representation of objects required in canning out the designs 

 of engineers, architects, and mechanics — whether as the means whereby such 

 designs are first studied, and afterwards matured — as guides for the resident 

 superintendents and workmen — or for being preserved as records of what has 

 been executed, and studies for those who may be engaged in similar under- 

 takings. 



He then proceeds to elucidate the advantages peculiarly possessed by mo- 

 dels for demonstrating practical results in Geology and Mining, dividing the 

 subject into six heads, as follows : 



1. On the application of modelling to geological and mining purposes. 



2. On the materials to be employed. 



3. On the mode of construction. 



4. On the scales to be employed. 



5. On the objects to be represented. 



6. On the use of geological models, and the connexion of the subject with 

 civil engineering. 



1. A large number of plans and sections is usually required to elucidate 

 with clearness the geology of a district, and the nature and extent of mining 

 operations; and few departments of practical science admit of greater im- 

 provement than the art of delineating mining plans in connexion with geolo- 

 gical features. 



Much ingenuity has been exercised in representing the undulating surface 

 of countries either by the process called "relief-engraving, (proccde Collas) 

 or as in the Ordnance Maps of England and Wales, and Mr. Greenough's re- 

 cent edition of his Geological Map : but even in comparison with these a 

 model affords a more correct idea. Hence models in rebef are more pecu- 

 liarly applicable in all cases where it is desirable to comprehend at once the 

 relations of the several parts, and it is evidently still better adapted to explain 

 the geological conditions ; especially when it is required to show the relative 

 position of various rocks, their inclination, thickness, extent, and the disturb- 

 ances to which they have been subjected, which could only be understood by 

 comparing together a number of drawings. 



To those interested in mining, therefore, the easiest mode of conveying 

 ideas is i)y modelling. This was illustrated by two models of the Forest of 

 Dean, and by reference to Mr. Jordan's model of the Dolcoath mine, now in 

 the Museum of Economic Geology. 



Materiak for models. — 2. The first material for forming a model which 

 naturally occurs to the mind is clay, pins and wires lieing used to define the 

 principal elevations. Plaster of Paris lias occasionally been used, and is well 

 adapted for solid forms, where the edges are not exposed to injury; but its 

 brittleness and contraction in drying are objectionable. Papier Mache is a 

 more elegant and durable material, but the expense of the requisite moulds 

 prevents its general use. Coloured wax is adapted for small models not sub- 

 ject to be handled. Pottery appears to possess more requisites, but many 

 corresponding disadvantages. Of all the materials which the author has em- 

 ployed, he found none so generally useful as well-seasoned wood, whether for 

 the facility with which the requisite forms are attained, for durability, for 

 portraying different strata by various-coloured woods, or for comparative 

 economy. 



Mode of construction. — 3. The mode of constructing geological models had 

 keen briefly alluded to by the author on a preceding occasion.* It is more 



* Journal, Vol. III., page 347. 



fully described in the present communication, and was illustrated by complete 

 models, and the detached parts for forming them purposely made on a large 

 scale. 



The plan of the district being divided by lines at given distances apart, into 

 a certain number of squares, a series of thin slips of wood are made to inter- 

 sect each other, corresponding to the lines so drawn — upon these slips the 

 profile of the surface and the positions of the strata are delineated, when it is 

 intended that the model when complete shall he dissected ; the compartments 

 are then filled in with wood, and carved down to the lines upon the slips i 

 the several strata thus rest upon the subordinate beds, and can be detached 

 in a mass or in comjiartments ; these being geologically coloured, convey an 

 ■accurate idea of the relative positions of the strata, and display with the ut- 

 most clearness the mining operations in each. This system is applicable to 

 any extent : and the operation of forming the model is so simple, that a skil- 

 ful workman at once comprehends and executes unerringly the instructions 

 given him by the engineer or surveyor, as the accuracy entirely depends upon 

 the profile which is drawn upon the slips. The author considers lime-tree or 

 plane to be the most suitable wood for the purpose ; but in the construction 

 of small models for showing peculiar geological features or disturbances of 

 strata, he uses various coloured woods : as an illustration of which he showed 

 a series of twelve models, which (with a printed description*) arc now in the 

 Museum of the Institution. These contain 579 pieces of wood, one of them 

 consisting of 130 pieces. By fitting the parallel layers of wood together, and 

 arranging them in conformity with sections of strata of tlie carboniferous 

 limestones and coal measures of the north of England, he illustrates the for- 

 mation of that district, and the nature of its dislocations, &c. better than can 

 be done by any number of plans and sections. 



4. Scales to be employed. — Attention is drawn at some length to the pro- 

 portion to be observed between the horizontal and vertical scales, and the 

 relative merits of corresponding and dissimilar horizontal and vertical scales 

 fully examined, illustrating the positions by tv.o models nf the Forest of Dean, 

 in one of which the vertical is enlarged to three times that of the horizontal 

 scale ; while the other has the scales exactly alike. For tlie conventional 

 purpose of giving an idea of a country such as would be formed by a general 

 observer passing through it, the former model appeared best adapted ; but in 

 a scientific point of view the latter had a decided advantage, being based on 

 geometrical truth, aud conveying an exact knowledge of the real, but not of 

 the apparent relations of the surfaces, and other objects represented. 



5. Objects to be represented. — Models had hitherto been chiefly used for 

 conveying impressions of tracts of the surfaces of countries, or for displaying 

 the minute tracery and proportions of buildings. The author's views have 

 been more especially directed to introducing the construction of models for 

 geological and mining purposes, for which he considers them peculiarly 

 adapted. 



The series of models now presented to the Institution, contains examples 

 of various geological phenomena of regular stratification — interruption by 

 slips, faults, and dykes — the effects of denudations in exposing to view the 

 various strata — the deceptive appearance of the course of mineral veins on the 

 surface — the intersection of veins — and many other details which are inti- 

 mately connected with practical mining. 



6. Models used in civil engineering. — The author then proceeds to describe 

 his view of the uses of such models, and the connexion of the subject with 

 civil engineering. 



He considers that by them a practical knowledge of geology may be attained 

 by the civil engineer, and that such knowledge is indispensable for his guid- 

 ance in many of the works he is called upon to undertake in the exercise of 

 his profession. It is to an engineer that the merit is justly due of having, by 

 efficiently labouring to establish English geology on a firm basis, acquired the 

 title of " Father of Geology," which has been generally conceded to the late 

 Mr. William Smith. 



The avocations of the civil engineer peculiarly qualify him for an observant 

 geologist ; and being called upon to visit so many diflferent districts, the re- 

 marks be might make would be replete with instruction. These observations 

 might be illustrated more efficiently by models than by any other means ; at 

 the same time they might be made to answer another purpose — that of de- 

 monstrating to the owners of mineral property tlie advantage or the futility 

 of commencing researches or mining speculations. 



Plans do not admit of such certainty of definition as modelling, and no re- 

 gular system of planning mining districts has yet been generally practised, by 

 which the engineer can judge of the probable results of the operations which 

 he is often called upon to direct. .\s a record of mining operations, models 

 of this kind are pre-eminently valuable ; the exact position not only of the 

 mineral veins and the strata are clearly shown, but the quantities extracted 

 are registered, and a guide for future proceedings is established. The author 

 contends that it is a duty to secure, while it is in our power, sucli records of 

 mining operations as may enable us and our successors really to exhaust 

 whatever minerals can be worked with advantage. 



.\s being in some degree connected with the subject under discussion. Dr. 

 Buckland described a mode used by Sir John Robison, for obtaining moulds 

 for plaster casts. The object, of which the mould was required, was immersed 

 in a mixture of common glue, dissolved in brewers' sweet wort of about the 

 consistency of thick cream, and allowed to remain until the mass became 



* Description nf a series of Geological Models, &c. By Tbos. Sopi\ilh' 

 F.G.S., &c. 12mo. Newcastle, 1841. 



