On the surface, most of this book is a record of how a series of cases evolved.
Literal
Superficially, this-book [possessive-の] most [topic-は] series [possessive-の] cases [possessive-の] changes [object-を] recorded thing [copula-である].
表面上 ('on the surface, ostensibly') sets up an implicit contrast with what lies beneath. 一連の事例の変遷 is a dense compound: 'the evolution of a series of cases.' 記録したものである uses もの as a formal nominalizer.