So far I seem to see a muddy or rather a sandy and sea depositing a thin series of regular bedded strata that are apt to be more decidably fossiliferous near the top. Under nor- mal conditions these seem to go into the struc- tureless clay (without plants or fossils, no bedding) and then wet sand and underclay (but not a fire clay) followed by coal. This is followed by land conditions, stream action that at first is de- graded cutting out channels, and then as degraded eroding widely not only the channels but also the marine beds. This is the condition in some cases but in others the section does not end in coal, or the sandstone may be followed by the struc- tureless clay. In other words in some cases the complete cycle does not take place but the marine invasions only follow one another at irregular intervals. To work out this matter the entire Pitts- bug area needs to be studied in the light of cycles of marine invasions, falling off of the shallow seas that in turn hand into struc- tureless clay, underclay and coal beds.