Saratoga Springs, New York
These layered formations are called stromatolites. In the ocean, sticky mats of bacteria and photosynthetic cyanobacteria trapped minerals and marine sediments. Bacteria continued to grow through the sediment, adding new layers. Sometimes fossils of the bacteria are preserved in the layers.
Stromatolites are still forming today in water too salty for snails and other grazing animals that would eat the bacteria.