chicago is located in between a coalfield and southern italy ndiana. iron comes from minnesota by both. chicago becomes the center of the steel industry in north america, along with pittsburgh. if you chart tghehe heights of chicago buildings, you see this whole generation of structures that leavesps up in 1890 after the refining process. leaps up because of legacy building codes. it leaps up between 15-20 stories for a good henumber of years. this is the old colony building on south dearborn. it uses a technique called a portal frame. it literally makes a monolithic connection between the steel columns are and the steel girders there. can see on the plan at the left that this replaces very thick sheer walls with skinny steel elements. you can also see that these elements can be tunneled through , you can build an office within the steel portal frame. that would be the only indication that you have this sheer wall and steel surrounding you. maybe a more direct translation of the realm road bridge -- railroad bridge is the masonic temple built in 1892,