Few people who drive to Woburn by way of Main Street realize, when they near the Woburn - Wilmington line, that they are driving through an ancient volcano.
Alongside the road is a cliff of basaltic rock. On top, where it may be seen in springtime, is a slight depression, which fills with water in the spring rains. This is the throat of an ancient volcano, up which was thrown hundreds of thousands of tons of molten lava, all of this having been hundreds of millions years ago.
There is no danger that the old volcano will ever erupt. It can be recognized for what it is only by persons trained in geology.
The history of the land which is now Wilmington began about 500 million years ago when what is now New England emerged from the ancient seas. Beneath the land which emerged, there was hot molten material known as magma, which kept trying to force its way to the surface. It would explore and find cracks, and then cool into enormous masses of igneous rock —rock which we today call granite.
The Quincy granites were formed at this time, as were granites all over New England. The type and grade of granite depended entirely on how close to the earth’s surface the molten magmas were able to get. If the magma was close to the surface, it cooled rapidly and formed a fine granite. If it did not get too close, it took longer to cool, and became coarse granite.
In the period of which we are writing, there was no Boston Harbor. It was yet to be made by the sinking of the Boston Basin, but it was as a direct result of that sinking that the volcanoes of Eastern Massachusetts were formed volcanoes in what is now Woburn, Winchester, Reading and Wilmington.
After the granites of which we have spoken had been formed there was a new geologic era in what is now the Boston suburbs, one in which the pudding stones of Roxbury were formed. The seas had again covered the land. Slates were formed in some places, from clays that were deposited on the bottom of that sea. In Wilmington, the soils that were deposited became schist, although not much of it exists today. That which does can mostly be found in South Wilmington from Wood Hill, over by the Burlington line, to Suncrest Acres, off West Street.
Schist is a soft stone which breaks easily into layers, an important feature, for it was this tendency together with others which led to the bankruptcy of a Nevada firm which tried to drill through the rocks of Wilmington’s volcano.
The hard coals of eastern Pennsylvania and the soft coals of western Pennsylvania and other regions were laid down during this same period, in which the pudding stones and schists were laid down in New England. Hence, the period is known as the Carboniferous Period.
When Boston sank
All of what today is Boston Harbor and the nearby cities once sank for thousands of feet, as the result of the weights of rocks in the area. The hole which resulted (and which has since nearly filled) can easily be marked off, in such places as Malden, Arlington and the Blue Hills.
The sinking of the land in and near Boston was a gradual process which took thousands of years. There was great stress and strain in the nearby hills. Cracks and curves appeared in the rocks.
Through these cracks, the molten rock beneath found a way to escape to the surface, and dozens of volcanoes appeared around Boston.
In the vicinity of Woburn, there were dozens of volcanoes, all pouring thousands of tons of lava and basalt upon the surface of the earth. Three volcanoes surround what is now Woburn Center. Horn Pond Mountain, now the reservoir of the City of Woburn, was a volcano. Today’s pond is in the old volcano mouth. The hill known as Blueberry Hill, on the Woburn - Winchester line, was a volcano. In the early to mid 1900’s, a quarry there provided hundreds of thousands of tons of rock for road building and railroads in eastern Massachusetts.
The northernmost of these volcanoes was just north of the Woburn - Wilmington line, today called Cook’s Hill.
It is a mere shadow of its former self, for the ice ages, which began about one million years ago, ground down what had been an imposing mountain into a small hill but the lava rock, the basalt, and the throat of the volcano can still be seen.
The most interesting point to be seen without climbing the hill is the cut where Route 38 runs through the hill. This cut was done about 1927, when Main Street was relocated. Previously, the road ran around the hill and around a pond known as Squaw Pond, which was filled in at that time.
The name Squaw Pond arose from the accidental killing of an Indian woman there in 1705, which resulted in the Harnden massacre but that is another story.
The contracting firm which took the job of cutting through Cook’s Hill and building the new road went bankrupt because of the nature of the rock left by the volcano. Because the hill is a mixture of granite, schist and basalt, the drills refused to go into the hard rock and instead bent and turned into the softer schist. Unable to maintain its drills and unable to finish the job, the company went bankrupt.
Atop the hill for many years, there was a stone chapel, built by a Greek - American. He had built it with the intention of it becoming an Orthodox Church. But it was abandoned, and during Prohibition it became a hangout for bootleggers.