The Brownstone Chronicles, Part 39: A Well-documented LSB Variety | Emmanuel United Methodist Church (1891), Evanston, Illinois, USA

Facing north-northeastward and looking at the church’s façade (southern elevation).

LSB is an abbreviation for Lake Superior Brownstone.

To architectural historians, this house of worship is of special interest because it’s one of the last designs of John Wellborn Root, the tragically short-lived architect who with Daniel Burnham produced some of the Windy City’s great masterpieces, including the Monadnock Building and the Rookery. But geologists have plenty of reason to focus their energies on Emmanuel Methodist, too.

Having recently discussed in this series a pair of LSB buildings on the Lake Forest College campus whose stone cannot be identified unequivocally, it’s a pleasure to turn to this Gothic Revival edifice in the certain knowledge we know what it’s made of. For its main exterior stone is unusually well documented.

Typically described in the historical literature as “Ashland Stone,” it is in fact the type of LSB known as Chequamegon Sandstone. That’s pronounced “shu-WAH-muh-gun.”

The marketing name of this striking rock type derives from the fact it was produced by the Ashland Brown Stone Company, based in the far-northern-Wisconsin city of that name. However, the firm’s quarries were located even farther north, on Stockton Island, which these days is part of Apostle Islands National Lakeshore. Once a bustling production center, this pine-studded isle now boasts a permanent population of about two dozen black bears periodically visited by necessarily intrepid human hikers and campers.

The stratigraphic unit that hosts this rock, the Chequamegon Formation, is the youngest portion of the Bayfield Group. This thick accumulation of clastic sedimentary beds sits atop the Oronto Group, also sedimentary, which in turn rests on the vast pile of volcanic flows erupted into the Midcontinent Rift.

A 2013 study of the detrital zircons it contains gives the Chequamegon a maximum depositional age of 1.035 Ga. This indicates that it is either very late Mesoproterozoic or Neoproterozoic. I’ll get into its mineralogy in close-ups to follow.

One thing about this brownstone variety that is clear even from this distance is that it has here accumulated a considerable amount of carbonaceous soot, biofilms, or both. These deposits are known collectively in the preservation trade as black crusting. They provide plenty of subject matter for persons interested in what I call fuligology, the study of stone weathering and the buildup of materials on surfaces.

Reference cited above:

- Craddock, John P., Alex Konstantinou, Jeffrey D. Vervoort, Karl R. Wirth, Cam Davidson, Lee Finley-Blasi, Natalie A. Juda, and Erin Walker. “Detrital Zircon Provenance of the Mesoproterozoic Midcontinent Rift, Lake Superior Region, U.S.A.” Journal of Geology 121:1, 57-73 (January 2013).

To see the other photos and descriptions of this series, visit
The Brownstone Chronicles album.

Taken in: United States / Illinois / Evanston Township / Evanston (show map)

Taken on: February 5, 2019

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architectural_geology

architecture

church

geology

illinois

masonry

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Evanston, Illinois

Emmanuel United Methodist Church

John Wellborn Root

Burnham & Root

Lake Superior Brownstone

brownstone

Chequamegon Sandstone

Chequamegon Formation

Bayfield Group

building stone

building materials

black crusts

Midcontinent Rift « less

Sets appears in: • Architectural Geology of Northeastern Illinois Exclusive of Chicago • The Beauty of Building Materials more » • The Brownstone Chronicles • Fuligology: The Science of Soot, Crusts, & Biofilms • MCR: Homage to the Midcontinent Rift • Natural History: Illinois « less

Camera: NIKON COOLPIX A10, f/3.6, 1/320 sec, 6mm, ISO 80 (more info) (hide info)

Camera:	NIKON COOLPIX A10
Aperture:	f/3.6
Exposure Time:	0.003 sec (1/320)
Focal Length:	6mm
ISO:	80
Exposure Bias:	0 EV
Flash:	Off, Did not fire
Exposure Program:	Program AE
Metering Mode:	Multi-segment
White Balance:	Auto
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