JIM THOMPSON’S INFLUENCE ON CONNECTICUT VALLEY GEOLOGY – 1946 TO PRESENT

In a long history, Jim Thompson became a master at understanding and tracing stratigraphic units, paleontology, and fold hinges to form an image of complex major structures. Although his contributions to mineralogy and petrology are better known, geology in the Connecticut Valley was his constant obsession.

Beginning in 1946, Jim helped George Moore map the Keene-Brattleboro area, NH-VT; he in the NH part of Mt. Grace; Jarvis Hadley the MA part. Then began a thesis in the Ludlow Quad., VT, completed 1950, in tandem with his friend John Rosenfeld in Saxtons River. Working E to the Connecticut, his NH experience paid in mapping Skitchewaug Mtn. (1954 NEIGC), the birth of the fold nappe theory. After Skitchewaug, more fossils were found in the sillimanite zone near Claremont (1958) and a new interpretation was made of the Bernardston, MA locality (1958), that the section is inverted, related to the Skitchewaug Nappe. Jim's NH knowledge influenced Rosenfeld and Eaton, to map NH strata near Middletown, CT (1958 NEIGC).

I entered Harvard fall 1958, to map with Billings and Thompson. Jim told me to look at Hadley's Mt. Grace map (1949) and see if it made sense. I did, and it did not. I drove through the area and told Jim I didn’t see much outcrop. His reply: "That is why the road is there", which proved perfectly correct. Thus began a task lasting >50 years. By 1962 I was teaching at U. Mass., Amherst, with easy field access. A volume was planned for Billings’ 1968 retirement. Jim enlisted me, Tom Clifford, and Newell Trask (1964), to write and illustrate a story of the Connecticut Valley nappes, leading to wide discussion. In 1966 Jim and I confronted a unit I called "gray schist member of the Partridge". Jim laid hands on the outcrop, saying "Oh rock, tell us your origin and age". That afternoon we found a new conglomerate belt separating this from Partridge, "proving" this gray schist was Littleton, which it remained to ~1984. Metamorphism, then thought Lower Devonian, was controversially related to level in the nappes.

Thompson and Rosenfeld (1979) recognized four, not three, fold nappes. Rangeley sequence strata were found ~1984-91 to be thrust west over the Bronson Hill sequence, with thrusts truncating fold nappes, and "gray Partridge" changed from Littleton to Rangeley. Geochronology ~1990-98 indicated ~4 metamorphic episodes, not one.