Boulders as examples of two-stage forms - Landforms and Geology of Granite Terrains - page 85

(c)

(d)

Figure 5.4. Corestone set in grus and exposed (c) Near Tampin, West Malaysia; (d) in the recently excavated

margins of the highway Lugo-Madrid near Lugo, Galicia northwestern Spain.

Their essentially near-surface occurrence, and a concomitant though not invariable diminution
in degree of rounding and increase in size of spheroidal masses with depth, suggest that most such
boulders are related to processes active at or near the land surface rather than to primary magmatic
or to hydrothermal effects, and are due to descending meteoric waters.
That they are due to differential weathering attack beneath the land surface was recognized as
long ago as 1791 by Hassenfratz (1791) ( Fig. 5.6a s ee also 5.6b), who, commenting on exposures
he had observed in the southern Massif Central, wrote:
“…on aperçoit tous les intermédiares entre un bloc de granit dur contenu & enchassé
dans la masse totale du granit friable & un bloc entièrement degagé.” (Hassenfratz,
1791, p. 101).