HAMMER-HEAD SYNCLINE

As the ideas of superimposed folding developed much later, Heron in 1934 was unable to afford an explanation of this unique structural pattern in terms of the superimposed folding. If the early folds are recumbent to reclined, the mushroom pattern is generally observed in profiles of late folds which are subvertical sections in the field. If the early folds are steeply reclined, the outcrop pattern can be noticed on subhorizontal subplanar surfaces. The tightness of the mushrooms (i.e., how far their "tips" come closer to the "stem") depends upon the tightness and degree of amplification of late folds. The conspicuous mushrooms are better seen in deeper sections than in shallower ones because folds become progressively tight with depth as shown in clay model experiments by Holmes and Reynolds (1954).