Early Cast Iron Pot

I recently purchased this cast iron pot at a local thrift store for $35.00. I did not know anything about it, but liked it. I have tried to find out any info on it with no success. The pot is cast iron and has no visible seams. It does have what I was told is a GATE(raised ridge on the bottom). It does 3 QT on the bottom as well as a makers mark S & T. It is 7 inches tall and is 9 1/2 inches wide. I do not know if the lid is original as it seems to be made of a lighter tin like material. I was wondering if anyone could give me an idea as to the age of it, as well as the name of the maker and did I get a good deal for $35.00?