An. Unrecognised Agent in the Deforviation of Bocks. 401 



again I think the principle of the bending slab of marble comes 

 to our help. Instead of a confused crack like that produced in the 

 Enon pebbles, due to an irregularly distributed pressure, we have 

 sharp lines, which can be explained by the grains in the line of 

 fracture being gradually deformed in the direction of definite zones 

 of flow ill the clay matrix. By the accumulation of these effects the 

 coherence of the particles was at length broken, and separation of 

 the laminae produced. 



How great a part in general deformation on the globe this 

 insidious slow-acting agent plays, is impossible to estimate at 

 present, but I think from what we have seen above it must always be 

 at work, and, side by side with denudation, tends to reduce all 

 inequalities on the earth's surface to one dead level. If its action is 

 not always to be detected in the rocks, it is one of the chief agents 

 by which the destruction of erections made by human hands is 

 accomplished. 



