Ok let us now hope for the best image loading :::
I don't understand what the fourth hallmark is for. The makers mark is for "John Main." The date letter code is for 1740 (although, to be honest, even this does not look exactly like the image in the list of date letters for Edinburgh, but it is closest to 1740). The GEO hallmark is the assay master hallmark which only lasted a few years due to a dispute in the hallmarking office at the time. The fourth hallmark, I do not understand. Is it for a provincial town, or is it perhaps another mark which I am not familiar with? I will get better pics of that mark, as it is very difficult to distinguish.