Stoneholes 17-20 Parchmarks - 50 years ago

Back in July I noticed some parchmarks at Stonehenge which were the first indications that there are stoneholes for the missing stones 17 and 18 and also showed the stoneholes for stones  19 and 20  - see this post for more details.

I bought a postcard today which dates from 1959 which also shows these parchmarks, I think they have often shown up and they were never recognized for what they are. Last year they had been there for some time before the penny dropped with me.

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