F. C. van Heurn was a chemical engineer (scheikundig ingenieur) formerly attached to the Avros proefstation at Medan, and author of studies on Sumatran soils.
Assessment of Temiang soils
In his Studiën betreffende den bodem van Sumatra, quoted by Dr. R. Broersma on page 103, Van Heurn wrote about Temiang: the tertiary hill country of Tamiang distinguishes itself from the mountain of same formation because at surface it consists mainly of clays and claystones, while marls or sandstones, represented as sandy hills, are in minority. The little sandy parts are as infertile as the sandy tertiary soils of Bengkalis, the clays have proven to possess excellent properties for European cultures with proper drainage.
Broersma questioned the proof, asking how those clays proved it, perhaps through existing plantings that were of too small extent.
See Also
Source
Atjeh als land voor handel en bedrijf, by Dr. R. Broersma, Gebrs. Cohen, Utrecht, 1925, pp. 10-11.