Complex sentence: Modern revision of the geologic sciences has restricted formations to lithologies, because lithological units are formed by depositional environments, some of which may persist for hundreds of millions of years and will transgress chronostratigraphic intervals or fossil-based methods of correlating rocks.
Split into simpler sentences: Modern revision of the geologic sciences has restricted formations to lithologies, because lithological units are formed by depositional environments, some of which may persist for hundreds of millions of years. Some of these will transgress chronostratigraphic intervals or fossil-based methods of correlating rocks.