As the rift valley opened in Avalon, it soon became filled with sediments which later formed the Roxbury Conglomerate. These rock formations were created between 570 and 550 million years ago, when Avalon was near the South Pole (Skehan). The rocks of Newton belong to a single sequence of volcanic and sedimentary deposits formed during Devonian time or about 350 to 400 million years ago (Skehan, J, and Barton). The bedrock is made up of sedimentary rock Roxbury Conglomerate or "Puddingstone."
Roxbury Conglomerate appears everywhere throughout the Reservation. Conglomerate is a course-grained clastic sedimentary rock that is poorly-sorted. The conglomerate in Hammond Pond Reservation contains quartzite, granite and felsite pebbles which are rounded to sub-rounded in shape (Skehan, J, and Barton). In some areas of Hammond Pond, there is sandstone embedded in the Conglomerate.
The rocks in the area have been estimated to have formed during Proterozoic Z and possibly Early Cambrian from the Avalon Terrane (570 to 550 million years ago) when Avalon was near the South Pole. The Conglomerate formed after the Laurentide Glacier retreated around 14,000 years ago (Skehan, J, and Barton). When the sediment is first deposited, there are lots of open spaces or pores. Cement can affect the amount of pore space that is left in a rock as it solidifies. Conglomerates usually have significant pore space and they are generally a good rock to act as a reservoir for ground water, natural gas and petroleum (Skehan, J, and Barton).
The rocks in the area have been estimated to have formed during Proterozoic Z and possibly Early Cambrian from the Avalon Terrane (570 to 550 million years ago) when Avalon was near the South Pole. The Conglomerate formed after the Laurentide Glacier retreated around 14,000 years ago (Skehan, J, and Barton). When the sediment is first deposited, there are lots of open spaces or pores. Cement can affect the amount of pore space that is left in a rock as it solidifies. Conglomerates usually have significant pore space and they are generally a good rock to act as a reservoir for ground water, natural gas and petroleum (Skehan, J, and Barton).
Weathering
In Hammond Pond Reservation, many different types of weathering occur. There are signs of both chemical and mechanical weathering. Chemical weathering includes oxidation and organic acids. Mechanical weathering includes organic activity, ice/frost wedging, sheeting, joints, exfoliation, and abrasion. Chemical weathering includes hydrolysis, oxidation, and organic acids.
Mechanical Weathering
Organic activity occurs when animals can burrow and scour away at rock, or by root wedging, meaning that the tree pries the rock apart. Much of the visible organic activity at Hammond Pond is root wedging due to the plentiful trees.
Frost/ice wedging is when liquid water seeps into a crack and freezes and expands (by 9%). This forces the crack apart, eventually shattering the rock.
When pressure is removed from a rock (by removing overlying material) the rock creates cracks called joints. Once the cracks are parallel to the surface, layers of rock form called sheeting. When the sheets fall off, it is called exfoliation.
Chemical Weathering
Hydrolysis occurs when water reacts with minerals changing the mineral composition to include H+ or OH-. Overall, hydrolysis was not the most common type of weathering I saw.
At Hammond Pond, oxidation was pretty common. Oxidation occurs when oxygen (dissolved in water) reacts with a metal often resulting in a color change. Most of the oxidized rocks I saw were slightly orange, meaning that they had rusted.
Glacial Features:
An erosional feature left behind from the Laurentide glacier are striations. Striations are scratched on the surface of a rock caused by sediment frozen in the bottom of the glacier being dragged across bedrock. These tell you which way the glacier was going