You have an interesting cartridge belt. I looked in several of my reference books and have it kind of narrowed down to a couple of different models.
At first glance it looks like a M1903 cartridge belt because of the easily recognized "unpuckered" bottom, but the M1903 only had 9 pockets. Also, looks like yours has lift-the-dot fasteners which were not utilized until 1917 and afterwards. Lastly, the belt is too narrow for a M1903.
Since it has 10 pockets and other features noted above, and after looking at the chart in "The M1903 Springfield Rifle and it's variants" by Joe Poyer, and reviewing the information in Bruce Canfield's "A Collectors Guide to the '03 Springfield", I would suggest you potentially have a M1917. Of the 16 or so variants of the cartridge belt issued for the M1903 rifle, only three are of the 10 pocket variety.
The cartridge belts produced prior to 1914 had a smooth, non rimmed, snap button with an eagle insignia on each pocket. The belts made from 1914 to early 1917 had a similar eagle button on each pocket but the button had a rim aournd the outside of it. The belts produced from about mid-1917 on had the familiar lift-the-dot fastener.
Each pocket of the cartridge belt was intended to hold two five round "clips" of ammunitino. Some belts will have a divider in each pocket while others, mainly later belts, will have a strap with a snap fastener to seperate the clips in each pocket. The M1938 belt, designed to be issued with either the M1903 or M1 rifle, was intended to hold either two five round '03 clips or one eight round Garand clip.
The M1938 cartridge belt was of the 12 pocket variety. Interestingly, most belts issued during WWII were actually 10 pocket M1928 belts designed for the M1903, and both M1923 and M1938 belts were manufactured during WWII.
Again, yours appears similar to a M1917, but the unpuckered pockets throw it off a bit, and it doesn't quite seem to fit the description of the M1923 either. Interesting that I don't see any markings either . . . even well worn USGI issue belts and cartridge pouches will usually show indications of the original ink markings.