My Slag Lamp

This lamp has been in my family for many years, but I dont know anything about it other than it is old (early 1900's is my best guess). It is 22 inches high, and the shade is 17 1/2 inches wide. Everything appears to be glass and brass, no manufacturing info anywhere I can see. I would greatly appreciate any help with information as to its age and history. I am 40 and this was my grandmothers parents lamp, so that is all I have to go on time frame wise