Couple Items I've Found

[dsb]

The light colored stone found on Arsenal island between iowa and illinois. The other in north east iowa from pipeline creek crossing. Thanks for looking.

[jasong]

Cool, white one I thought was some bolt impressions at first haha. Looking closer, definitely marine fossils though probably in limestone - no clue what fossils though in specific, not my strong point. Looks like some clams, and some plant stems and/or coral? 

The yellow rock is some iron stained quartz, probably glacial?

[dsb]

Thanks i didn't know much about them.  Your probably right about the yellow one.  Don't see much but limestone around here but just to the west there are glacial smooth rounded stones in the fields.  This came from that type area but from a 6 foot deep trench thru a creek bed.  The white stone with fossils is really smooth and very hard,  was in better shape but spent a few winters outside.

[Geologyhound]

Definitely have some common crinoid columnals in the white limestone.  They typically look like a fossilized stack of small poker chips. 😄 This type of crinoid was a filter feeder and was anchored to the sea bottom by the column “spine”. 

I concur the yellowish one looks like quartzite.