History

The original sedimentary rocks forming the basement of this area were sandstones, limestones, dolostones, and shale.  These sediments were deposited in a shallow sea that covered the region.  Although these rocks date back to about 1.3 billion years ago,  some of the area rocks contain the mineral zircon that dates back to 2.7 billion years ago.  The presence of these rocks indicates that the sediments that formed these rocks originated on a much older landmass (Roecker).

The Adirondack region was part of the ancient Grenville Mountains which arose 1.2 billion years ago during the Proterozoic Era.  The Grenville orogeny was the result of the collision between proto-North America and the continent known as Baltica.  The Grenville area was caught in between and was thrust onto the side of proto-North America.  The collision buried the Adirondack rocks.  The Grenville Mountain range that resulted stretched from Canada to Mexico.  This is the earliest evidence of mountain building in the Northeast (Paleontological Research Association).
 

Baltica approaches and collides with North America,
Grenville belt pushed onto side of North America
(Paleontological Research Association)used by permission
http://www.priweb.org/ed/TFGuide/NE/geo_history/ne_geohist_main2.htm


During the Late Cambrian period, the area was gradually submerged beneath a shallow sea.  Trilobite fossils were abundant in the newly deposited Sandstones.  This deposition can be viewed at the outskirts of the Adirondack region today.

More sediments were deposited up to the Pennsylvanian period, but only major deposits of rock from the Middle Ordovician and younger remain.

The Grenville Mountains were eventually weathered to a flat plain.  At that time, only a few traces from the Cambrian and Odovician periods remained.  This was only because some areas had depressed lower than its surroundings and were spared from erosion that took place (Roecker).
 

Flat plains of sediments over basement rock
(Boquet River)used by permission
http://www.boquetriver.org/bedrock.html


The region was then covered with a thick layer of sediment during the latter part of the Paleozoic Era.  About 20 million years ago, during the Tertiary period, the basement rock pushed up through the layer of sediment and Grenville rock.
 

Basement rock pushing up through sediments
(Boquet River)used by permission
http://www.boquetriver.org/bedrock.html


As the younger, softer sediment was eroded away, the harder Grenville rock was exposed and eventually formed a central mountain mass (Boquet River Association).
 

Exposures of Grenville-aged rocks
(Paleontological Research Association)used by permission
http://www.priweb.org/ed/TFGuide/NE/geo_history/ne_geohist_main2.htm


Stream and glacial erosion has carved out the mountain range we see today.  The Adirondacks arecurrently continue to rise.  Measurments in the 1980s proved the area is rising at a rate of 2 to 3 mm per year (Roecker).
 
 
 

Back to Table of Contents
Glaciation