Contact relations play an important part in Structural Geology. However, contacts are often easily eroded and poorly exposed. We are going to examine the Holyoke basalt in order to determine if it is an extrusive rock as is widely thought.
Extrusive rocks are concordant with the sedimentary strata upon which they are deposited.
The purpose of this lab is to determine if the basal contact of the Holyoke basalt is concordant with the underlying sandstones and conglomerates of the East Berlin Formation. Initially horizontal layering is exposed in the East Berlin Formation. However, there is no layering in the Holyoke basalt and its basal contact is rarely exposed. In the field carefully determine the location of 3 points along the base of the Holyoke basalt. Use your topographic map s, the altimeter and the GPS receiver to locate these 3 points.