FIGURE 1. Mat finish.
From the following article:
Palaeontology: Modern life in ancient mats
Michael M. Tice
Nature 452, 40-41(6 March 2008)
doi:10.1038/452040a
Noffke et al.5 find features in 2.9-billion-year-old rocks from the Pongola Supergroup in South Africa that are similar to those caused by microbial mats in intertidal zones today (left, fossil Pongola feature; right, contemporary feature for comparison): a, uprooted and redeposited mat chips; b, overfolded rock chips; c, oscillation cracks.