Historic Photos of Washington, D.C. and Niagra Falls

Since my Dad's death, I have been going through some very old photographs that have been at the farm  forever.  My Great Grandfather was a pretty accomplished hobbyist photographer.  He held many jobs in his lifetime but, one of his favorites was a job with the Santa Fe Railroad.  Dad thought he was a ticket agent.  One of the incredible perks of a job like that was that he got to travel anywhere on the Santa Fe for free. 

These photographs were taken on original glass slides in the late 1800's, or early 1900's.   

I'm pretty sure the above(and below) were taken in Washington, D.C. I can't imagine how the above photograph was taken. Do you see the Washington Memorial in the background? How was it taken from this height? 

 

   

Does anyone know what this monument is?

I think maybe this is the train station.

Can you see these ladies in their long skirts, and the men in their suits and hats?  I think this was taken at Niagra Falls.

There is nothing written on the backs of any of them.  It's a reminder to me to write even faintly the date, and who is in the photo, and where it was taken.