A NEW STRUCTURAL ANALYSIS OF TWO TEACHING LOCALITIES: THACHER PARK AND HOFFMANS FAULT

This paper presents recent work on two structurally complex regions: Thacher Park (Albany County, NY), and Hoffmans Fault (Schenectady County, NY). Both sites are considered prime field trip localities, and were visited extensively by the present author during his own undergraduate education. However, recent analyses have shown that the generally accepted eplanations for features observed may not be entirely correct.

Hoffmans Fault in Wolf Hollow has long been considered an excellent locality for observing fault drag on a major normal structure. Indeed, beds of the Schenectady formation are seen to increase in dip from near horizontal to 30 degrees or more as one approaches the fault plane. However, while the location of folding does suggest that fault drag might be responsible, detailed regional mapping shows that the folded beds actually belongs to one limb of an anticline-syncline pair that has been transected by the fault.

In like manner, Thacher Park has long been considered an excellent locality for studying the Helderberg Limestones in near wedding cake perfection. However, detailed mapping of the park has shown that the sequence is cut by at least three low angle thrust faults, and at least a dozen splays, making the park an even better locality for studying the effects of thrust repetition and omission.

Prime examples of localities worth visiting during future field trips are included in this paper.