18 SHRINKAGE FISSURES OLDER ROCKS. 



directions. Hence in well drawn out building con- 

 tracts, it is specified that all stones should be laid 

 on their " quarry bed," as otherwise the settlement 

 of the masonry will be uneven. Dry rocks or stones 

 that have been for some time quarried contract less 

 than freshly quarried rocks. It may therefore be 

 suggested that stones, before being used for building 

 purposes, ought to be allowed to lose their quarry 

 water ; for if fresh moist stones are put into a build- 

 ing along with well dried ones, no matter how neatly 

 or finely the joints are laid, these must eventually 

 open more or less in certain places. Open joints are 

 often attributed to bad building, when in reality the 

 fault may have been in the mixture of stones in dif- 

 ferent stages of contraction. This often occurs in 

 buildings ; new fresh quarried and cut stones being 

 used as quoins and such like, while the intervening 

 work may be built of old stones, which have been 

 drying for years in another building. Different kinds 

 of stones contract in different degrees. This sub- 

 ject, however, seems not to have attracted sufficient 

 attention, as we have been unable to find the records 

 of any experiments on the contraction of rocks. 



Eocks in situ must form by their contraction 

 joint-lines ; and as in the recent deposits, so also in 

 the older rock masses, there are minor joints only 

 affecting one or a few associated beds, and master 

 joints that cut through many strata. Minor joints 



