The Stevens Family built Sybil’s Cave in 1832 as a whimsical addition to their land in Hoboken. The Cave housed a natural spring and is the earliest building in Hoboken that humans developed. By the middle of the 19th century, the Cave had become a popular leisure location within walking distance of the central business district of Hoboken. Alongside the Cave was a café with an outdoor seating area that served drinks. The Cave became the property of the Stevens Institute when the Stevens family homestead was converted into the Stevens Institute. Beginning in the early 20th century, the Cave was sometimes available to the general public. By the latter half of the 20th century, the structure was entirely obscured by rubble from previous construction.
The Cave was found again in 2007, and the City of Hoboken was responsible for its cleanup. The city only did a little investigation before erecting a new cast stone arch and fence that identifies the Cave but does not allow access.
The New Jersey Historical Trust awarded a grant to the Hoboken Historical Museum in 2009 for developing a geo-ecological plan to mitigate the environmental changes caused by the recent opening of the Cave. With this grant, the museum was able to create a plan for the appropriate use of the Cave as well as interpretive programming. The interior was subjected to a thorough archeological excavation so that as much information as feasible could be gleaned from the site with as little disruption as possible while still paying close regard to the site’s continued viability. The structural stability of the Cave, as well as the purity of the spring water, were both evaluated by an engineering company that was contracted for this purpose.
Most artificial caves and rock shelters in New Jersey are less than fifty feet long. The more extensive instances are almost always found in either limestone or marble, although the smaller examples may be found in a wide range of other rocks. According to “Caves of New Jersey” Bulletin 70, which the Department of Environmental Protection published,
New Jersey Geological Survey, Sybil’s Cave, also known as Castle Point Mine, can be found in the USGS (15-minute) Jersey City quadrangle (40 o – 44.7′ N 74 o – 01.5′ W) within the serpentine rock Formation. This information was gleaned from the location of the Cave.
In the 19th century, one of Hoboken’s most popular tourist destinations was a spring that could be found within Sybil’s Cave. The Cave opened its doors in 1832, but it was closed in the 1880s owing to concerns raised by the New Jersey Health Department over water purity. Subsequently, the Cave was stuffed with mud, concrete, and bits of serpentine rock during the 1930s.
The Cave was reopened to the public in October of 2008 by the Mayor of Hoboken, who also oversaw the construction of a new arch at the Cave’s entrance. The Cave has a width of about 17 feet and a depth of about 19 feet. It has four square pillars, 2 feet by 2 feet each, and a cistern holding spring water. The Cave has a horseshoe-shaped entrance about 9 feet wide at the bottom and 13 feet wide at the center/spring line of the Cave. The entry to the Cave’s square-shaped cistern may be found in the exact middle of the cavern.
The Coastal Plain Province, the Piedmont Province, the Highland Province, and the Valley and Ridge Province are the four physiographic provinces that may be found in New Jersey (see Figure 3 for an illustration of these provinces). The Piedmont Province has sandstones, argillites, shales, serpentine, conglomerates, basaltic lava flows, and diabase intrusions. Sybil’s Cave may be found in Hudson County, part of the Piedmont Province. The entrance to Sybil’s Cave was dug out of a magnificent cliff of serpentine rock that is situated between the city of Hoboken and the Hudson River.
Provinces of New Jersey’s Physiographic Structure (NJ Geological Survey)
On March 12, 2010, men named Robert Foster and David Webster from the Hoboken Historical Museum and Mr. Saad Cheema from Black & Veatch traveled to inspect the site. The following broad observations can be made after visually examining the Cave in the field, mapping the rock formations, analyzing rock samples, and conducting a desk study literature review.
1. As shown in Figures 4 and 5, the rock at the Cave’s entrance is extensively broken and dips at an acute angle (between 60 and 70 degrees). 2. As seen in Figure 6, the pillars supporting the Cave’s ceiling look stressed and have signs of spalling at the roof/pillar contact.
2. As illustrated in Figure 7, the rock fragments on the Cave’s floor reveal that the ceiling has been spalling over time.
3. The rock samples taken during the site inspection show that a serpentine rock type is present, which is sometimes linked to asbestos concentration. This rock character may need further research.
4. The heavily worn, broken rock near the cave opening includes soil that was very unstable and damp at the time of the site inspection. Figure 8 depicts the dry rock wall near the Cave’s entrance (photo not taken during the site visit).
WATER QUALITY ANALYSIS
On December 15, 2010, a surface water sample was obtained from the natural cistern inside Sybil’s Cave. This cistern has a depth of around 1 meter and 3 feet. The model was taken at a depth roughly 5 centimeters (about 2 inches) below the water’s surface. The results of the field measurements made from the water sample using a portable calibrated water quality meter are shown in Table 1. (YSI 6820 MP).
RECOMMENDATIONS
The steps listed below should be taken for Sybil’s Cave to be once again accessible to the general public.
1. The Cave must be rehabilitated by adding internal and exterior rock support using shotcrete and rock bolts.
2. A local geotechnical company (Jenny Engineering Corporation, 2 Edison Pl, Springfield, NJ 07081; phone:973-379-6699; Dawn Underground Engineering INC, 10 Village Court, Hazlet, NJ 07730; phone:732-739-8840) should be hired to keep an eye on the Cave’s rock stability over time. This helps determine how stable the rock mass is in the Cave.
3. People should not be allowed to consume water from cisterns due to coliform bacteria. Still, there are no additional health issues related to the water, and other than consumption, direct contact is not anticipated to pose a substantial health risk.
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