The Cockley Beds aren't actually cockle beds but death assemblages i.e. the shells are not in their original life position. Instead what you're looking at is piles of empty shell, all jumbled together, to form great shell banks that coated the shallow tropical sea floor.

The Cockley Bed as it might have appeared in Swindon's warm Jurassic Sea.

The broken up shells again suggest a sea that was probably quite rough and stormy at times.

It may even have been the result of Jurassic hurricanes that came through the area and stirred everything up leaving bits of broken shell all over the seabed.

Below the Cockley beds are the Glauconitic Beds which are sandy limestone layers containing glauconite. Glauconite gives a green colour to fresh surfaces and cropped up in shallow warm seas about 155 million years ago. Although there are no seashells in this layer the presence of glauconite shows that it was still a marine environment.

...carry on walking along the Old Town Rail Path