Darwin's Boulders

A geologist colleague has just brought to my attention this interesting article in Geoscientist that describes Darwin's field trip to Wales in 1842 and his correct description of several boulders as glacial erratics:
http://www.geolsoc.org.uk/gsl/geoscientist/features/page4451.html

BUT I will leave it to you the reader to find the howler in the very first line of the otherwise excellent article!