372 PLINY'S NATURAL HISTORY. [Pook XXXVI. 



purposes, arc subject to no deterioration by lapse of time : 

 moulds, too, are made from them, for the purpose of fusing 

 copper. There is a green silex, also, which offers a most 

 powerful resistance to the action of lire, but is never found in 

 any large quantities, and, in all cases, in an isolated form, and 

 not as a constituent part of solid rock. Of the other kinds, 

 the pale silex is but rarely used for erections : being of globu- 

 lar form, it is not liable to injury, but at the same time it is 

 insecure for building purposes, unless it is well braced and 

 tightly held together. Xor yet docs river silex oifer any 

 greater security, for it always has the appearance of being 

 wet. 



CHAP. 50. OTHER STONES USKD FOIl BUILDING. 



\Vhen the nature of stone is doubtful, the proper precaution 

 is, to quarry it in summer, and not to use it for building be- 

 fore the end of a couple of years, leaving it in the meantime to 

 be well seasoned by the weather. The slabs which have been 

 damaged will be found to be better suited for the foundations 

 under ground : while those, on the other hand, which have re- 

 mained uninjured, may be employed with safety, and exposed 

 to the open air even. 



CHAP. 51. THE VARIOUS METHODS OP BUILDING. 



The Greeks construct party- walls, resembling those of brick- 

 work, of hard stone or of silex, squared. This kind of stone- 

 work is what they call "isodomon,' MI itbeing"pseudisodomon" 43 

 when the wall is built of materials of unequal dimensions. 

 A third kind of stonework is called " empleeton," 43 the two 

 exteriors only being made with regularity, the rest of the 

 material being thrown in at random. It is necessary that 

 the stones should lie over one another alternately, in such a 

 way that the middle of one stone meets the point of junction 

 of the two below it ; and this, too, in the middle of the wall, 

 if possible ; but if not, at all events, at the sides. When the 

 middle of the wall is filled up with broken stones, the work 

 is known as " diatoichon."" . 



41 * 4 Built of stones of equal size." 



42 " Built of stones of unequal sizet." 

 45 ' Filled up work," apparently. 



44 The reading is very doubtful here- for the word seems to mean, in 

 Gre(k, " From one wall to another." JDiamicton M " Mixed up," is 

 another reading. 



