History of Newton, MAGeneral HistoryMuch of the bedrock is either volcanic or sedimentary, however, some earthquake fissure fillings do exist. Much of Newton's bedrock history begins in the Devonian period from 416 million to 358 million years ago (Skehan, 3). The sedimentary rocks include Cambridge Argillite, Slate, and Roxbury Conglomerate, whereas those which are volcanic include Mattapan Volcanics and Brighton Volcanics (Skehan, 3).
In Pre-Cambrian times, it is suspected that igneous activity created a bedrock layer of Dedham Granodiorite, a plutonic rock often identified between felsic and intermediate (Skehan, 3). Granodiorite has been found in the area and is very likely to be a lower layer within the bedrock, covered by Mattapan Volcanics, puddingstone, and slate (Skehan, 3). The geologic activity during and after the Devonian period left around 5000 feet of sedimentary rock and other deposits which likely cover the Dedham Granodiorite today.
During the Pre-Pleistocene period, a large lake covered much of the Boston area (Kaye, 2). Argillite, a sedimentary rock similar to, but harder than shale or slate, was deposited as clay and gravel material. This later created Roxbury Conglomerate, or “puddingstone” (Kaye, 2). Therefore it can be suspected that Cambridge Slate and puddingstone have much in common. The alternating layers of slate and conglomerate also suggest that there was an alternation in grain sizes throughout different depositional periods over a long period of time (Skehan, 4).
It is uncertain how many volcanoes existed in close proximity to one another, but it is certain that at least one major volcano had existed (Kaye, 2-3). Volcanic ash covered much of the plains and was carried to the lake by rivers (Kaye, 3). Slate in Cambridge and Somerville shows evidence of volcanic ash deposits, but the main depositional areas of volcanic rocks were in places at which conglomerate had been formed (Skehan, 4). Conglomerate is often deposited in rivers, which is also where much of the ash would have ended up (Skehan, 4). If the ash traveled all the way to the lake, it could have been deposited with the Cambridge Slate. Some of the faults found in Newton formed as the alpine mountains of east-central Massachusetts were created (Skehan, 4). Two features created were the Boston Border Fault and the Shawmut anticline of Newton (Skehan, 4). In addition, about 150 million years ago, an earthquake occurred in Massachusetts where the fissures were filled with dike rocks (Skehan, 3). Many of the youngest depositions in Newton are from glaciers (Skehan, 4). For example, the local drumlins were left after the last glaciation twelve thousand years ago (Kaye, 7). These drumlins include Oak Hill, Bald Pate Hill, Chestnut Hill, and Mount Ida (Kaye, 6). When glacial crevasses or ice tunnels form, meltwater carries sediment into these openings which fills them. Once inside, the sediment becomes trapped and chokes the channels. When the glacier retreats and melts away, the sand and gravel inside is deposited on the ground as narrow ridges called eskers. Examples of these can be found at Edmands Park, Waban, Auburndale, Newton Centre, and Newtonville (Skehan, 6). During the glacial retreat, outwash plains formed from the meltwater streams as well (Skehan, 6). In addition, numerous ponds and lakes were created (Kaye, 7). Also, very little vegetation flourished during this period (Kaye, 7).
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