How does one distinguish rock strata by geologic composition?

Answer 1

Rock Identification Tables


These tables will help you identify almost any rock you're likely to find. First determine whether your rock is igneous, sedimentary or metamorphic. The quick way to tell is:

Igneous: little texture or layering; mostly black, white and/or gray minerals; may look like lava (About Igneous Rocks)
Sedimentary: layers of sandy or clayey rock (strata); tends to split along layers; mostly brown or gray; may have fossils and water or wind marks (About Sedimentary Rocks)
Metamorphic: layers of light and dark minerals (foliation), often wavy; various colors; glittery from mica (About Metamorphic Rocks)
Then start in the left column of the appropriate table and work your way across. Follow the links to pictures and more information. If you don't find a match, try another of the three big types.

Grain Size has two values: "coarse" grains are visible, and the minerals can usually be identified using a magnifier; "fine" grains are invisible to the naked eye and cannot be identified with a magnifier. The cutoff is about 0.1 millimeter, between sand size and silt size. (using a magnifier)

Hardness has three values: "hard" rock scratches glass, which usually signifies the minerals quartz or feldspar (Mohs hardness 6-7 and up); "soft" rock does not scratch glass but scratches fingernails (Mohs 3-5); "very soft" rock can be scratched with a fingernail (Mohs 1-2). All igneous rocks are hard.

for the table check the site
http://geology.about.com/library/bl/blrockident_tables.htm

Answer 2

Limestones can be identified by the shells and fossils in them. Chalk indicates another era. Coloured layers indicate dry desert conditions. Streaks of sulphur indicate a stagnant reducing environment. There are many many more types of rock and a trained eye can spot which one is which.