Classicly

A section of a long and splendid literature can be most conveniently treated in one of two ways. It can be divided as one cuts a currant cake or a Gruyère cheese, taking the currants (or the holes) as they come. Or it can be divided as one cuts wood—along the grain: if one thinks that there is a grain. But the two are never the same: the names never come in the same order in actual time as they come in any serious study of a spirit or a tendency. The critic who wishes to move onward with the life of an epoch, must be always running backwards and forwards among its mere dates; just as a branch bends back and forth continually; yet the grain  in the branch runs true like an unbroken river.