Complex sentence: The geology of Djibouti consists largely Miocene to Holocene volcanic rocks around which are more recent alluvial deposits with coral on the coast, as well as Cenozoic sedimentary.
Split into simpler sentences: The geology of Djibouti consists largely of volcanic rocks from the Miocene to Holocene epochs. There are more recent alluvial deposits with coral on the coast, as well as Cenozoic sedimentary.