From L. C. Wedgwood 20 January 
6 Q. A. St.
Out of 25 worm-holes probed with a blunt wire between Jan 6 & 14 on different slopes for a few inches, 8 came to the surface nearly vertical to the slope; the rest at various angles.1
I will try some more, and when I have dug some more trenches will send the result about furrows
Gives results of probing worm-holes with wire.
Please cite as
Darwin Correspondence Project, “Letter no. 8169,” accessed on 30 March 2017, http://www.darwinproject.ac.uk/DCP-LETT-8169