This causes the lava to flow as many tube-like blobs, which eventually overlie each other. This photo is of some thinly bedded, very fine-grained sedimentary rocks. Evidence indicates that they were deposited in a deep marine environment, in water depths between 750m and 1000m deep. The water was very still, allowing these very fine sediments to slowly accumulate on the sea floor. Examining these sediments under a microscope revealed that they contained abundant radiolarian fossils.
Radiolarians are beautiful, microscopic, single-celled animals that built skeletons out of silica.
See the picture below. The abundance of rads indicates that the sediments accumulated very slowly. The slower the deposition, the more rads are able to die and be deposited within a single layer. A Scanning Electron Microscope photograph of a radiolarian. The conditions on the sea floor were usually very calm, but occasionally you get sub-marine avalanches that rush into the area with a lot of power, ripping up part of the sea floor sediments as they go.