Treadle sewing machines are awesome! I love mine and do all my sewing on it. I will never go back to electric. The sewing machines of the 1850's were very primitive and they were chain stitch technology, with a single thread, not the double thread lock stitch, which is the type that you have. You can date your machine very easily with the serial number. It will be located either on the bobbin compartment, the oval badge, or on the base of the machine head. It appears from the configuration of the bobbin compartment that yours probably has a round bobbin and not a vibrating shuttle, which I think is going to put it in the 1920's. If it has a shuttle (bullet shaped case inside the bobbin compartment which holds spindle shaped bobbins) you'll be about 1890 at the earliest through the 1920's. But the easy way is just to look up the serial number.