Discussion of Table 1 data from Logan:

The Carbonaceous shales: There are from 11-13 of these in this section of strata.  There are no Stigmaria recorded in any of them.  Most of these are situated below and/or between the coals; however, in two instances they are (both) above and below "underclays."  These are most likely shales that simply contain high amounts of organic matter.

The Sandstones and Argillaceous Sandstones: There are five of these recorded by Logan in this section, three of which bear the name "understone;" however, a fourth one: a "rough gray sandstone," may also merit such a description.  Three of these contain "Stigmaria;" and could refer to roots or rootlets of trees other than the Sigillaria.  One bed contains  Stigmaria ficoides, and one contains both "branches and leaves of  Stigmaria ficoides."

Arenaceous Shales: These are sandy shales.  They are called "Underclays," not because they are clays, but because they contain roots and/or rootlets, and are often found beneath coal seams.

If we ignore the Carbonaceous shales which do not contain roots, then there are 29 potential (ancient) seat-earth/soils  in this section.  Of these, only one is said to contain both "branches and leaves" (i.e. rootlets) "of Stigmaria ficoides."  However, this  "rough gray" (7 foot thick)  "sandstone" is, itself, under a 2 foot thick "argillo-arenaceous shale" (underclay) "with stigmariae."   Note that Logan does not say that the leaves are connected to these branches; however, even if they were, it is still a reasonable assumption that the roots below with "branches and leaves" were not connected to the stigmariae (roots or rootlets) in the bed above and therefore may not be a soil at all.  The most that one could say is that they might have been connected, and thus this may have been an ancient soil horizon.  Therefore, out of 29 potential (understone/clay) soil horizons, it is doubtful that any of represent in situ soils.