Please could you re-post that as a new topic.
(If we allow follow-ons in the same topic, topics can get too long, and subsequent searches can become less useful through dilution with irrelevant information.)
The one on the left is a septarian nodule.
The one on the right might be one as well; can't tell without seeing inside it.
Superficially, from this viewpoint, it is just a rounded cobble/pebble with planar bedding running through it - appearing as ovals where the bedding interests the surface. You could break it in half to see if there is something different at its centre, and maybe see if there is concentric zoning as well. If so, it would probably be a concretion, and if it contains radiating or ramifying veins, it could be a septarian nodule.
Septarian nodules are discussed in this article on concretions
There is a lot of misinformation on septarian nodules, eg.http://www.bestcrystals.com/septarian.htm,http://www.madagascarminerals.com/metaphysic_of_septarian_physi.cfm
and much of the misinformation is copied between different sites.
Also, the word 'septum' has nothing to do with 'sept' meaning seven.