Quartz reefs (sometimes called quartz veins) vary in depth, size, continuity, curvature and their angles from the vertical - as well as the amount of gold contained within them. Garling was pointing out that Bendigo's belief in "anticipation of gold at depth" was wrong.
Garling should have said that Morning Star's quartz reefs (gold-bearing) were quite different from those (non-gold bearing quartz reefs) that Bendigo chose to mine.