Let’s get a little scientific here. Jamaican rocks include the oldest which are known as Cretaceous. The Cretaceous limestone can be found in upper Clarendon and in Westmoreland. What is even more interesting is that this Cretaceous limestone contains a wealth of rudist material. Rudists were a group of moluscs, closely related to the cockles, which became very large and highly specialized. This group is extinct in the world today.
Other igneous and metamorphic rocks are believed by some geologists to be basal and probably pre-Mesozoic. While others consider these rocks to be somewhat intrusive and of Cretaceous or post-Cretaceous age.
This is getting really spooky. A dinosaur bone was actually found among other fossils in the Cretaceous shales of the St. Ann Great River Valley. Cretaceous limestone, bearing marine fossils, occurs just 300 feet (91m) below the summit of Blue Mountain Peak.
There is the occurrence of Eocene formations (the Blue Mountain series) of the Blue Mountain and the Port Royal Mountains. These formations consists largely of conglomerates, shales, and sandstone, along with intrusive igneous materials of sills and dykes.