Cayman has a unique position in geology, sitting on the edge of the tectonic plates for North America and the Caribbean. The islands’ formation and geologic history are of special interest to Brian Jones, a Canadian professor who has visited the country numerous times over the past 30 years to study the rocks that make up the Cayman Islands.
He was on island earlier this month to mark Geology Week and share his new book with teachers, officials and the public.
Despite its name, ironshore is actually the softest rock in the Cayman Islands. The rock at Hell is white on the inside, and the most similar rock formation found elsewhere is the Stone Forest in China’s Yunnan Province. Sometime between the 1990s and today, boulders in East End weighing up to 10 tons moved 328 feet or more inland, most likely a demonstration of just how strong Hurricane Ivan was.
At Hell, there are a number of tall tales about how the unique jagged rocks got their form. Volcanoes and earthquakes had nothing to do with it. Microbes have been eating away at the limestone and dolomite, excreting acid as they bore into the rock, for millions of years, leaving the pinnacles and caverns that give Hell its characteristically craggy form. The black, sooty color comes from what’s left when the microscopic organisms die, along with deposits from plants growing in the rock.
Cayman’s unique geology has been included in a new textbook by Professor Jones from the University of Alberta and Professor Noel James from Queen’s University. Mr. Jones, who has done research and worked with the Water Authority in Cayman for decades, recently shared “Origin of Carbonate Sedimentary Rocks” with teachers and students to improve geology education.
Mr. Jones gave a lecture on what he calls “geotourism” while he was on Grand Cayman this month and explained some of his favorite geologic features around the islands.
Talking about Hell, Mr. Jones said, “It’s difficult to date.” He estimates the formation is 10 million to 15 million years old, but the stone is so soft that geologists can’t take a core sample to try to figure out a better date.
People touring the East End of the Brac might notice, high up on the rock bluffs, a notch in the rock, jutting in like a triangle. That notch actually shows where the sea level used to be, Mr. Jones said. That same wave-cut notch is visible around most high points around the islands.
Looking down into the ironshore covering much of the islands’ coasts, a close observer can see much of the black rock covered in fossils. One of the best fossil outcrops in the world, Mr. Jones said, is on the northwest coast just south of the Cayman Turtle Farm. He said researchers have identified 14 coral species dating back 125 million years.
Over by Pedro Castle, there are lots of coral fossils, dating to about 5 million years ago. The fossils there are from standalone coral species that lived in the sand. The modern equivalent is no longer found in the Caribbean, Mr. Jones said, but is seen around the Pacific Ocean.
Near the blowholes is another strange feature of Cayman geology. There are 52 boulders, weighing as much as 10 tons, sitting on the ground as it slopes up away from the coast. Mr. Jones dated one of the boulders, based on relatively modern coral found embedded in the rock, to between 1625 and 1688. Mr. Jones and his team’s theory is that a hurricane or tsunami picked up the rocks from the sea floor and dropped them in the bush. One important feature of the area, the professor noted, is that it is one of the few areas with no reef protecting the coast.
Mr. Jones and his team mapped these boulders in the early 1990s. He went back to check on them recently, but none were where they were supposed to be according to the map. The mammoth rocks had all moved between 300 feet and 500 feet away from the coast, climbing another 20 feet up from sea level.
“It was as if someone had taken the boulders and scraped them over the rock,” he said, and he could even see the tracks leading from down the hill. Mr. Jones said the only possible explanation is that the wind and waves of Hurricane Ivan pushed the boulders even further.