Simplify the following text for a Grade 7 native English-speaking person.
Original: The Blue Lias consists of a sequence of limestone and shale layers , laid down in latest Triassic and early Jurassic times , between 195 and 200 million years ago .
Simplified: The Blue Lias consists of a sequence of limestone and shale layers . It was laid down in late Triassic and early Jurassic times , between 195 and 200 million years ago .