The Missing Limestone Monolith of Stonehenge

In 1997 Dr. Olwen Williams-Thorpe claimed there was evidence for there having been a limestone monolith at Stonehenge, and it was in their previous paper:

Williams-Thorpe, O. ; Green, C. P. & Scourse, J. D. (1997). The Stonehenge bluestones: Discussion. Authors' reply. In _Science and Stonehenge_. pp. 315-318.

I can only find a claim to limestone fragments in what I take to be the previous paper. Am I missing something?

 Thorpe, Richard & Williams-Thorpe, Olwen & Jenkins, D. & Watson, J. & Ixer, Robert & Thomas, R.. (2014). The Geological Sources and Transport of the Bluestones of Stonehenge, Wiltshire, UK. Proceedings of the Prehistoric Society. 57. 103-157. 10.1017/S0079497X00004527. 

I think a few limestone fragments aren't enough to claim there was a monolith, presumably of the size of one of the standing stones. Is there anymore evidence?