Which building is known for being constructed in two distinct parts, one with heavy brick walls and the other with a steel frame?

The Monadnock Building is known for its unique architectural design that features two distinct construction methods. The southern portion of the building, completed in 1891, showcases heavy masonry with thick brick walls, reflecting the load-bearing construction style of the time. In contrast, the northern part, completed a year later, was built using a steel frame, which was a newer technology that allowed for more flexible and taller structures.

This combination of construction styles illustrates a significant transition in architectural practices during the late 19th century, where buildings were beginning to shift from traditional heavy masonry techniques to modern steel frame methods. The Monadnock Building serves as an important illustration of this evolution in building technology and design, making it a significant landmark in Chicago architecture.