There were many variations of chain, during the progression from the crosscut saw to the modern chainsaw.
The flat stuff is 'scratcher' chain. It was used before Joe Cox invented modern 'hooded' chain in 1946. Essentially, there were flights/groups of scoring cutters that scratched through the wood fibers. Saws ran slower, with lots of torque. Took a lot more skill to sharpen because the teeth needed to be jointed (same height), set (sideways projection), and filed at different angles.
The 'Y' chain is also a variation. It has multiple scoring cutters (like a manual crosscut saw) and fewer rakers (note that many people call the depth gauges on chains 'rakers', which causes confusion).
On modern chain, the side plates act as scoring cutters, and the top plates act as rakers, chipping out the wood fibers, forming the kerf. One of the big advantages claimed in the original patent is that they are much easier to sharpen.
There are some illustrations of older chains on Mike Acres 'Chain Saw Collectors Corner' website if you want to see more of these.
Philbert
