214 



DISCOVERY 



of niches and recesses in their steep and often broken 

 slopes which give plenty of shelter from the midday 

 sun. and which afford a view of the steep grassv side 

 of the next hillock. And there are many perpendicular 

 scarps where the side has, at some time or other, been 

 sharply cut away, which, from a little distance, look 

 like cliffs, and which would certainly give plenty of 

 shadow. 



Fig. 4 is a photograph of one of the wayside streams 

 just S. of Carpenedolo, which shows how quickly the 

 water runs over the pebbles, utterly unlike the stagnant 

 ditches of Pietole. And the reason for this is obvious, 

 namely that in the 27 English miles between Carpene- 

 dolo and Mantua the water has to fall more than 100 

 metres, that is to say, more than 330 feet, which is a 

 very different thing from i metre in 9 miles. Some 

 of these little running streams have sluices in them to 

 hold up the water in a pool whence it can be diverted 

 into the meadows by the side, as the last line of 

 Eclogue III describes. 



The last pictures are of the spot on the ridge of Car- 

 penedolo with the River Chiese in front (Fig. 5), where 

 it seems to me likeliest that Vergil's farm stood, and 

 another (Fig. 6) showing the view of the lower Alps, 

 rising sharply (see the map) behind Brescia, which are 

 always visible from Calvisano. On a certain number of 

 specially clear days in the year the great snowy heights 

 of the Adamello group are themselves visible behind ; 

 and when they are not visible, they are always covered 

 by a great mass of torn and broken cloud which lends 

 to the distant view just such an element of mystery 

 and wonder as lovers of Vergil know to be the most 

 characteristic thing in all his descriptions of nature. 



Full authorities for the statements contained in this paper 

 in which a good many disputable matters have been treatt'd 

 with brevity, will be found in a paper published in the Bulletin 

 of the John Rylands Library (vol. vii, January 1923) under the 

 title, " Where was Vergil's Farm ? " I thank my colleague, 

 Mr, W. A.Gould, B.A., cordially for the trouble he has gen- 

 erously taken in preparing the map. 



Modem Industries — III 



Brick-making in the Midlands 



By R. C. Skyring Walters, B.Sc, 

 Assoc. M. Inst. C.E. 



The object of this paper is to describe the brick-making 

 industries of the Midlands, in particular that of the 

 district between Peterborough and Bedford. In this 

 district are situated, perhaps, the largest establishments 

 in the country for making ordinary common building- 

 bricks, known as " Flettons " — the origin of such 



works being due to the presence here of clay known as 

 the " Oxford clay," which is particularly well suited 

 both as regards quality and quantity for the manu- 

 facture of bricks. 



The criterion for a clay which will be suitable for 

 making ordinary common bricks is not easUy defined, 

 as a pure clay (which contains about 40 per cent, of 

 alumina. 50 per cent, of silica, and 10 per cent, of water) 

 is unsuitable for brick-making ; and comparatively 

 little is known of the impurities found in natural clays 

 which go to make up a good brick. Chemically, brick- 

 making is not an exact science, for neither the chemical 

 arrangement of the oxides, alumina and silica, nor the 

 effect of the impurities in a clay upon its physical pro- 

 perties, such as its plasticity when moistened, nor its 

 behaviour when calcined, nor its variable colour, is 

 fully understood. 



But it is definitely known that brick-making material 

 has been originally formed from the decomposition of 

 rocks, such as granite, which contain felspar (the 

 opaque constituent of granite), the potash or other 

 base of the felspar having been taken away and the 

 alumino-silicic acid,' i.e., clay having been left. It 

 is known that the presence of sand in clay tends to 

 prevent the clay from shrinking when burnt, raises 

 the temperature required for burning, and reduces 

 plasticity ; whereas the presence of lime in a clay 

 causes shrinkage, a lower fusion-point, and an increase 

 m plasticity. Hence chalk may be added to " lean " 

 siliceous clavs ; and, on the other hand, sand to " foul " 

 or very plastic limy clays. Ferric oxide induces the 

 red colour ; magnesia, the yellow. Iron pyrites tends 

 to split, and certain salts tend to warp or twist or melt, 

 the bricks when they are burnt, and these salts are 

 therefore detrimental. 



In short, the known chemistry of clays for brick- 

 making is at present not unlike that of cement some 

 thirty or forty years ago, and there is no doubt that 

 ere long chemists will discover as much about the 

 chemical reactions that occur when a piece of clay is 

 burnt as they know to-day of the reactions between 

 chalk and clay when they are calcined together for 

 making cement. At present the best test for a brick- 

 clay is its trial under the conditions under which it is 

 proposed to be manufactured into bricks on a large 

 scale. 



There are, however, certain physical and mechanical 

 properties of a suitable brick-making clay which may 

 be recognised in the field. A suitable clay — 



(i) Must be of uniform material, colour, and texture, 

 without patches of chalky or limy material (such as 

 is contained in man}' drift-clays). Such lime may 

 also be in the form of hard nodules, pebbles, fossO- 



' Alumino-silicic acid contains about 40 per cent, of alumina, 

 46 per cent, of silica, and 14 per cent, of water. 



