An Introduction to Geological Mapping through Building Stone

Wayne Powell
Brooklyn College, City University of New York
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project


Students examine "outcrops" of stone in the exterior of buildings in order to gain initial experience in making field descriptions of rocks, as well as in using field notes and photos to correlate outcrops and define rock units.

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This activity is designed for sophomore-level geology majors who live in an urban setting, and so have greater familiarity with an architectural environment than with a natural field environment, and who have a suite of commonly-used building stones available to examine in an accessible neighborhood.

Skills and concepts that students must have mastered

Basic identification of rocks, minerals, fossils, sedimentary structures, and structural fabrics are prerequisite skills.

How the activity is situated in the course

This assignment is offered either in a prerequisite course for a geological field methods class, or as an introductory exercise in a student's first field mapping course.


Content/concepts goals for this activity

Students will reinforce their ability to classify rocks, and identify rock components (minerals, fossils, fabrics).

Higher order thinking skills goals for this activity

Students will be able to be able to correlate spatially separated "outcrops" of rocks that belong to the same unit based on characterization of rock components.

Other skills goals for this activity

Students will be able to compose effective field descriptions of rocks, including sketches and references to field photographs.

Description of the activity/assignment

The burden that a typical three- to six-week field-methods course may place on students in terms of time (absence from work and family responsibilities) and money (cost of travel, cost of course, lost wages) can negatively affect learning, or even access to the course itself. This is particularly true for students in urban, non-residential colleges. One approach to addressing this issue is to design a field course in a modular fashion; essential skills are introduced and practiced in local settings; the skills are integrated and reinforced in a culminating "out-of-town" mapping project of reduced duration. This assignment is an example of one such pre-travel activity, in which students develop skills in outcrop description, analysis, and correlation/categorization with other outcrops.

Students are assigned map areas within a historic business neighborhood (e.g., Wall Street in Lower Manhattan) such that each assigned area has some overlap with those of other groups. In pairs or small groups, students are required to examine the stone(s) that comprise the outside lower-level of each building within the map area, and do the following:

  1. In field notebooks, fully describe the rock(s) exposed in each building.
  2. Determine how many unique stones are exposed in the map area.
  3. Identify which buildings are composed of the same stone (i.e., share the same mineralogical, textural, and/or paleontological characteristics, and so are likely quarried from approximately the same locality).
  4. Write a composite description of each distinct stone, emphasizing the features that help to distinguish each "unit" from the others exposed in the map area, and including photos that illustrate the diagnostic features and representative appearance of the rock. Classify each stone, and describe the conditions under which each unit formed.

The field work is conducted over a minimum of two days. During Day 1 students work through as much of the map area as they can, making detailed outcrop descriptions and some initial correlations between units. Subsequently, students meet as a class to discuss their observations, define criteria to distinguish units, and assign all outcrops from Day 1 into distinct units. On the second field day students begin re-examine key buildings from Day 1 to confirm or refute their proposed correlations. During the remainder of the day, students complete the coverage of their map area. Groups may choose to revisit their field area on their own time.

Determining whether students have met the goals

In class, students exchange descriptions of rock units (with photos removed) attempt to recognize their own units through the descriptions of their peers. By means of this informal comparison, students can gauge the completeness and quality of their own descriptions. Each group then revises their descriptions, inserts field photographs and corresponding references in the text, and drafts a summary table of addresses, rock units, and rock classifications. Final reports are graded based upon the completeness of descriptions and the accuracy of correlations. A penalty may be incurred for stylistic writing errors.

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