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Fig. 16. (See p. 3^7.) 



aa = Two halves of a layer of plaster fractured in the middle, and 



again a second time. 

 bb = Pieces broken off and forced up, 

 cc = Layer of flexible material above the plaster. 

 dd— Layer of flexible material below the plaster. 



Fig. 17. — Showing the same materials as in fig. 16. 

 hut more compressed. 



