Floors of high-side D&RGW gondolas?

I have been looking over a number of photos of D&RGW high-side gondolas. Many of them have a second layer of floorboards over the trucks. When I see them cut down and modified to a flatcar configuration, the extra floorboards appear to be missing. What was the purpose of this extra layer of floorboards over the trucks? I am assuming that it was to keep gravel and dust from dropping through the floor and onto the trucks? Would anything unwanted possibly seep through the floor cracks onto journal boxes and brakes? Or was it where a large portion of the load was placed when the cars were filled? Any helpful info would be great.

Thanks,

Jake Johnson