Sentence:  It will become apparent from the following discussion that some of the various structures which are grouped together as <WSD>cleavage</WSD> may correspond to a schistosity and/or foliation. Accordingly, Wilson defines "rock <WSD>cleavage</WSD>" (and schistosity) as a planar structure, usually distinct from stratification, which permits rocks to be fractured or cleaved into thin slices. Dennis (1977) defines <WSD>cleavage</WSD> as a set of closely spaced secondary, planar, parallel fabric elements that impart mechanical anisotropy to a rock without apparent loss of cohesion. This latter definition appears more precise; however, as we shall see, it presents many difficulties in dealing with those forms of <WSD>cleavage</WSD> which are mainly defined by foliation or by fractures. 
Meaning of the word marked with <WSD> tags:  The act of cleaving or the state of being cleft. (from 19th c.)