Conversations with Professor Prestwich #5
THE DEFORMATION OF ROCKS

Dear Geoneophytes,

Nothing has impressed me more during my long study of the earth than the copious evidences of profound deformation found in the Earth’s crust. My American colleague, Professor Claypole, estimates that in the Appalachian Mountains, 153 miles of crust have been compressed into a width of 65 miles. How did he come to this conclusion? Simply by assuming that all the sedimentary layers were originally horizontal and then unravelling all the folds and faults: in essence he straightened a crumpled rug, something most of us have done.

As students you must understand two things: (i) that the same forces which build mountains also deform the little details found in our rocks, and (ii) that the task of unravelling the complexity of our our great mountains is a game of chess played in three spatial dimensions but only understood if you can grasp the magnitude of geological time. I wish you a dreamless sleep, unencumbered by nightmares of rocks bending, twisting and ultimately crushing you. My colleague Charles Lapworth was almost driven insane by such dreams.

Cordially,

Joseph Prestwich