The Ohio site mentioned:



The use of Portage Quarry as a business dated back to the late 1800s when the limestone was highly valued for its level of dolomite. It was reported that there was no purer dolomite in the world. Dolomite was used for building stones and an aggregate in concrete and asphalt for roads. Geologists report that this type of Niagara limestone indicated that it originated as an enclosed or isolated portion of the sea basin.



That plus fertile soil will yeild those BG you see.