Dr. Hayden was one of the founders of the Maryland Academy of Sciences and served as its president in 1825. In 1820, as a pioneer geologist and botanist, he published the first general work on geology to be printed in the United States.
He discovered the mineral called Haydenite, obviously named after him. It's only been found in one place: the Jones Falls Valley which bisects Baltimore City. There have always been quarries along the Jones Falls, including one at Bare Hills. The specific quarry where Haydenite was found is at the intersection of the Jones Falls and Stoney Run, somewhere around North Avenue and Maryland Avenue.
Haydenite is an orange to golden brown chabazite with scalenohedral modifications and showing contact twinning. The chemical make up of Haydenite is (Ca,K2,Na2)2[Al2Si4O12]2 · 12H2O
The portrait of Dr. Hayden at the top of the page is by Rembrandt Peale, a famed Baltimore painter.