All editions of the Wiltshire Archaeological and Natural History Magazine (1855-2013) are freely available online at https://www.biodiversitylibrary.org/bibliography/12272
The passage below is in Vol X 1865 – it refers to a paper read by Cunnington at the Eleventh Annual meeting :
No. XXVIII. JULY, 1866. Vol. X.
Account of the Eleventh General Meeting, at Salisbury, 13th, 14th and 15th September, 1865
Mr. Cunnington F.G.S. next read a paper on " the Geology of the Stones of Stonehenge," in which he first pointed out the many erroneous statements which had been made on this subject, some having described the stones as foreign marble resembling that -of Carrara; others as formed of artificial matter, moulded to the original forms; and others again as a species of coarse freestone. These various statements having been satisfactorily refuted, he proceeded to explain that the outer circle and the large Trilithons at Stonehenge as well as the whole of the circles at Avebury, were composed of sarsen stones : the sarsens found so abundantly in Wiltshire, more especially in the Clatford valley of North Wilts, being the remains of sandy strata once lying above the chalk, the softer portions of which have been washed away, leaving these rocky masses on the surface. He then referred to the smaller circle and inner oval, and pronounced all these stones to be primary igneous rocks and of foreign origin, the altar stone is a fine-grained micaceous sandstone. From the facts adduced, Mr. Cunnington argued that Stonehenge was not originally erected either as a sepulchral monument, or as an astronomical calendar. This paper will however be found in extenso in the Magazine, and need not therefore be anticipated here.
Next to the final sentence “The paper will be found in extenso in the Magazine, and need not therefore be anticipated here.” Someone has written “Where?”
The same person (presumably) has written in the margin a few inches higher up “See Vol XVI – p71-74 –reported by Long”.
I have looked at the reference in Vol XVI which says “ But upon this subject, there is no one who deserves a hearing, and a more attentive hearing , too, than Mr Cunnington, F.G.S., who has devoted so much time and thought to the study of the geological character of the Wiltshire megalithic structures. He says, in a paper “on the geology of Stonehenge,” read at the Salisbury meeting of the Wilts Archaeological Society 1865: “We are indebted to Mr Prestwich, the treasurer of the Geological society, for the exact determination of the stratum from which the ‘Sarsens’ are derived (vide Journal of the Geological society).” (thanks to a volunteer library researcher for this)