Geology Reference
In-Depth Information
a massive photographic compendium of characteristic species from every geological time
since the Cambrian explosion.
RobertShrockwasagiftedteacherwithagentlesmile,anaturalwhoimbuedhisclasses
with humor and an unabashed passion for his profession. He taught in an avuncular style
by telling vivid stories of past times. He told of the chance horseback discovery a century
ago of the Burgess Shale in British Columbia, a 505-million-year-old site whose unpar-
alleled soft-bodied fossils were made famous in Stephen Jay Gould's Wonderful Life . He
described how cute fossils of little frogs were preserved in fine-grained silt in 300-million-
year-oldtreestumpsatJoggins,onNovaScotia'swesterncoast(thelittlefrogsjumpedinto
the hollowed-out stumps but couldn't jump out). He painted vivid pictures of 90 million
years ago, when a vast inland sea covered what is now the Great Plains of the American
Midwest—a sea where monster reptiles and squidlike ammonites vied for supremacy.
By a strange twist, my wife, Margee (then a senior at Wellesley College), and I wound
up being Bob Shrock's last two students. In the spring of 1970, student protests against the
Vietnam War turned angry; classes were disrupted and property destroyed. Given the per-
vasive distractions, MIT's administration gave students the option to take courses pass-fail
and thus skip final exams. Margee and I were the only two students to opt for a grade in
paleontology.Ourexhaustingfinalexam,administeredpiecemealoverthespaceofaweek,
was to identify every unknown specimen in a tray of a hundred fossils and then draw the
specimen by hand . Drawing from nature is admittedly a great way to hone observational
skills,butIwasnoartist.Eachpencilsketchwasamini-nightmare;ittookforeverandcon-
sumed more erasers than I can recall.
That was Bob Shrock's last paleontology class. The arrival of the eminent seismologist
Frank Press as the new department chairman in 1965 had marked a changing of the guard
andaswiftshifttoamorequantitativeandphysics-basedapproachtoEarthscience.Hand-
drawn fossils had no place in that modern world, where plate tectonics shifted curricula as
surely as it did continents.
Inspiredbythatfinalclass,MargeeandIspentmanyweekendscampingatnearbyfossil-
rich localities. Over the next few years, we collected fossil ferns in southern Massachu-
setts, corals in northeastern Pennsylvania, brachiopods in eastern New York, and trilobites
in northwestern Vermont. Shrock's course had taught us to see these fossils in a new con-
text. Each type of rock and each suite of fossils told a story of diverse ancient ecosystems.
Welearnedthatatanygiventime,severaldifferenttypesofrocks—differentfacies—are
being formed, each at a different place and depth of water. Sandstones form nearest the
beach in rough, shallow tidal zones. They feature populations of robust fossil clams and
snails with thick shells that could withstand the battering surf. Limestone, by contrast, rep-
resents ancient coral reefs and thus hosts a rich array of animal life—stalked crinoids, star-
fish, snails, brachiopods, and other groups that thrive in a protected sunlit lagoon. The
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