These are probably a species of the Crepidotus family of fungi. Quite small and delicate, with the largest cap only about the size of a ten pence piece. The name means “cracked ear” and grows on dead wood which in this case is likely to be birch. From the mixed woodland of around Slack’s Quarry near Great Ayton. Although not poisonous Crepidotus fungi are not considered edible.