This Edison Record is heavy and looks like it's close to a half inch thick.
There is no standard "A" or "B" side. Rather there is an "L" and "R" side.
This record may be a vertical cut.
I consulted Rust's American Record Label Book to see what he had to say. I wish I could say he was illuminating, but he barely mentioned the use of different recording technologies. It does appear, however, that Grey Gull issued lateral records as well as vertical ones in different numerical series. Some of the laterals were pressed from licensed Paramount masters. The laterals must have been pressed in some numbers, although I would infer from their relative rarity (I don't ever recall seeing one, myself) that they were not as numerous as the verticals, which you do encounter with some regularity, but not usually in large numbers. For what it is worth, Rust observes that Grey Gull labels were second only to Victors in American issues at British second-hand shoppes, leading him to speculate that large numbers were bought at a discount and imported when the company failed. Perhaps a disproportionate number of the laterals went overseas?
Are you sure about all Grey Gulls being vertical ? I had entered one of my Grey Gulls to the site, and it is marked "Lateral" on the label. It is titled "Sweet and Low" on side A, by the Harmoniser Quartette.
There is no "may" about it. The vast majority of all Edison records were vertical cut, that being the original recording technology that he invented. The cylinders and all of the heavy thick Edison Diamond Discs were vertical cut. Edison did not experiment with the lateral cut until the very end of his record-producing career, when he introduced what was known as the Needle Type record (readily identifiable by the reference on the label). The Grey Gull family of labels were also vertical cut (Grey Gull, Radiex, Madison, Van Dyke, an early Globe label, I think...) The earliest Gennetts were verticals, with lateral versions specially labeled, but by the time they'd adopted their well-known red and blue labels they had gone completely lateral.
You may get really unsatisfactory results if you attempt to play a vertical cut record, even with a 78 needle, unless you have a stylus that is specially suited to vertical cut playback. Such styli are usually sapphire styli (but then most 78 styli are) with a distinctly different profile than ordinary 78 needles. They are designed to get to the bottom of the groove where the vertical signal will be found, as opposed to straddling the two sides of the groove where the lateral cut signal is. and then to ride solidly in the groove rather than skate about from one wall to the other, which is what regular 78 styli often do because of the different dimensions of the grooves used in the different techniques. If you are looking for playback equipment to handle vertical records I suggest you look up Kurt Nauck's website for guidance on what to buy and where to find it.