Geology Garden dates back millions of years

A tour of the Class of 1957 Geology Garden is a virtual pass through time, tens of thousands, hundreds of thousands, millions, or even a billion years.

At rest outside of Hayden Hall, stretching from Smith Walk to 33rd Street, the stony and emerald path is spaced with boulders from the Earth’s many ages, some predating the dinosaurs.

The idea for the garden came from the mind of Hermann Pfefferkorn, a professor in the Department of Earth & Environmental Science in the School of Arts & Sciences, and was brought to life by donations from members of the Class of 1957.

“Our campus is such a beautiful park,” Pfefferkorn says. “There are so many interesting things. There are the sayings of Ben Franklin on Locust Walk. The many sculptures around campus. I wanted to introduce a little bit of science near our building.”

Ten boulders, donated by quarries in the southeastern Pennsylvania region, populate the garden and represent geology around Philadelphia from 25,000 to 1 billion years ago.

On the east side of Smith Walk, a gray boulder shows glacial markings that were created close to 25,000 years ago when large sections of North America were covered by a continental ice sheet.

A 200 million-year-old block of dark diabase was produced by volcanic eruptions during the last of Philadelphia’s volcanic age.

From the Devonian age, a 390 million-year-old, brownish gray hunk of sandstone contains a layer with fossils of shelled animals.

Pfefferkorn says the age of the blocks was determined with assistance from his geologist colleagues.

“You date these by two different methods,” he says. “One is by determining the age of the overlying rocks, and the other one is there are minerals in some of these rocks that can be directly dated with radioactivity.”

Three of the boulders are around 1 billion years old, including a gray granular rock with whitish, pink-ish bands that was formed when magna or molten rock intruded into older rocks, and a block of serpentinite from the Precambrian age.

The boulder closest to 33rd Street is the billion-year-old, rare greenish gneiss.

“This is a doozy,” Pfefferkorn says of the archaic mass. “It’s a beauty. It’s curved because it was distorted inside the Earth by forces in the Earth.”

Prehistoric boulders in the garden are joined by four plant communities, relatives of those that existed in North America in days past and represent vegetation of a particular era.

Young dawn redwoods, growing in the garden, were a dominant species in North America 45 million years ago. The garden’s small gingko forest is similar to those that existed on Earth 100 to 220 million years ago.

Pfefferkorn, who has a 298 million-year-old fern in his office and can see the Geology Garden from his window, says with renewed interest, he would like to expand the plot, adding more plants and four or five blocks from various points in time.

“There’s a beauty to geology,” he says. “Many of the rocks are beautiful, but also what the rocks have created on Earth is beautiful, and there is beauty in these fascinating stories of what all had to happen for it all to come together.”

The Geology Garden is one of the sites on the Discover Penn cell phone tour. Callers can listen to a recording about the boulders and plants, narrated by Pfefferkorn.

For more information on the tour, visit

Geology Garden