In short then, the geologist interprets and puts order into millions of years of history which can only be “read” as recorded in the rocks beneath our very feet. Of course, just looking at the rocks does not magically open the book of geologic history. This pamphlet is designed to sharpen your powers of observation and to help you in your interpretation of these observations. [Illustration: Figure 2. Thin-section of granite from Burke Mountain. The main minerals seen in this photograph are feldspar (light gray center right, marked with “F”); quartz (whitish, marked with “Q”); biotite (light gray, speckled appearance, marked with “B”). Note the interlocking nature of the minerals which make up this rock. Magnified 15 times, under crossed nicols.] THE ROCKS AND THEIR HISTORY The most conspicuous rock found in the park is _granite_.[1] Along the road which winds to the summit of Burke Mountain you will see several outcrops of the white or pinkish biotite granite (Fig. 4). This granite is well displayed in the summit parking area and along the trail to the observation tower (Figs. 3 and 5). A walk down the Bear Den Ski Trail also shows an abundance of granite outcrops (Figs. 6, 7, and 8). [Illustration: Figure 3. Speckled granite with inclusion of metamorphic rock. Black specks in granite are flakes of black biotite mica. Metamorphic inclusion, located just above the hammer head shows some reaction with the invading granite. Pieces of metamorphic rock were undermined by and dropped into the granite as it worked its way upward into these rocks. Picture taken a few yards west of the tower on top of Burke Mt.] While looking at some of the above-mentioned photographs, a second family of rocks is discovered (Figs. 3, 5, 6, 7, and 8; also, Figs. 9, 10, 11, and 16). In many places these rocks have a layered or banded appearance and in other places large lath-like crystals are common in some of the layers. In some areas these rocks are very heterogeneous in appearance and display distorted layers and profuse development of lath-like crystals (Figs. 12 and 13). These rocks belong to the second major family of rocks, the _Metamorphic_ rocks. The metamorphic rocks[2] seen in the park were originally _sedimentary_[3] rocks. These rocks belong to the Gile Mountain _Formation_[4] which was deposited during the _Devonian Period_ some 300 million years ago (see Geologic Time Scale[5], Fig. 14). So much for the two major families of rocks present in the park, the igneous and metamorphic rocks, and how to distinguish one from the other. Let us assume that you can now distinguish between the granite and the metamorphic rocks.