Sounds to me like it's a section of a larger volume:
On the Stone Circles of East Cornwall.
Gray, H
Archaeologia 61, 1908.
60pp, 6figs, 8b-w pls,Bound in contemporary card covers, these offprints include all original plates, last page in good facsimile, Please enquire for availability
That last bit suggests he's got more than one - photocopies??