If you have not read an original source but have read about it in another source and want to discuss it, you must reference the source you have actually viewed.
If possible, try and locate the original source yourself so you can refer to it directly. If not, the format for creating a Harvard reference for secondary references is:
Shuell (cited in Biggs and Tang 2011, p.97) puts forward the idea that…
This idea has been outlined.... (Shuell cited in Biggs and Tang 2011, p.97)
Reference List Examples:
You must fully reference the source you have actually read - Biggs and Tang in this example.
BIGGS, J. and C. TANG, 2011. Teaching for Quality Learning at University. 3rd ed. Maidenhead: Open University Press