Now this is a really super old photo of Washington from around 1857. Click on it for a much larger version to study it. I believe this is a view looking southeast, and the Washington Monument would be just out of the frame on the right.
Correct me if I’m mistaken. Also, you should be able to make out the Smithsonian in the distance.
Considering the time frame it looks like you can see parts of columns and other building materials from the additions that the
Something happened to my comment …but what got eaten was that these materials look to be the additions that the Architect of the Capitol was working on in the 1850s.
This ca 1855 photo from the Treasury building is on the Smithsonian website. More information about it is at: http://siarchives.si.edu/collections/siris_sic_9272
You are looking south west! looks like this might be taken on top of the Union station or building along North Capital and E street or FSt NW