More to Boston than "Puddingstone! “ EarthCache

The aim of this EarthCache is to begin to demonstrate the diversity of rocks used in downtown buildings, in a different way. You will need something to take a photograph and also a small piece of scrap paper.

So many of these great buildings are made from rock quarried locally.

This EarthCache allows you to compare and contrast other relatively “local stones” to the more widely known "Puddingstone"

BOSTON'S MOST WELL KNOWN ROCK

Roxbury Conglomerate, also informally known as Roxbury Puddingstone, is a name for a rock formation that forms the bedrock underlying most of Roxbury, Massachusetts, now part of the city of Boston. The rounded pebbles, and the sharp contrast in colours gives this type of conglomerate the appearance of a raisin or Christmas pudding.

Conglomerate is a sedimentary rock that forms when rounded gravel and other large fragments, called clasts, are cemented together by pressure and other processes:

1. Sediment deposition: Gravel and other clasts are deposited by water or glaciers.
2. Clasts are rounded: The clasts are rounded because they have been transported from their original source or have been in a high-energy environment for a long time.
3. Fine-grained sediments fill in spaces: Clay and sand fill in the spaces between the clasts.
4. Cementation: A chemical cementing substance, such as calcium carbonate, iron oxide, silica, or hardened clay, precipitates and binds the clasts together.
5. Compact rock: The result is a compact rock made up of rounded clasts surrounded by finer-grained sediments. 

Conglomerate forms in aquatic environments, such as rivers or coastlines, where strong currents help to form the rounded particles. The clasts can be made of a variety of different rocks or minerals, but the largest clasts must be rounded. 

It is a sedimentary rock. It was formed from weathering and erosion of pre-existing rocks, resulting in the formation of sediments and dissolved compounds in the water.

LESS WELL KNOWN 'LOCAL' ROCKS

Many other rocks quarried from the vicinity are igneous rocks, that were formed from the cooling of magmas. These Boston building stones are igneous, formed deep underground with larger crystals. Many are granites

Granite is a coarse-grained igneous rock that forms when magma cools and crystallizes deep within the Earth:

1. Magma: Granite forms from magma that's rich in silica and alkali metal oxides deep underground.
2. Cooling: The magma slowly cools and solidifies underground over a long period of time, allowing larger crystals to form.
3. Uplift: The granite is eventually uplifted to the surface as the volcanoes or mountains above it erode.

Logging tasks

At any one of the three locations take a picture with you, or a personal item in the foreground and your chosen building in the background . (REQUIRED)

THEN

Get a scrap of paper about 3” x  5” or 10 cms x 15cms Rip a hole out of  the centre. Write your caching name on it (See photo below)

At LOCATION 1:  Take a closer picture of the most widely known indigenous rock, Roxberry 'Puddingstone,'  placing your newly made ‘quadrat’ carefully against the stone to demonstate its character.

Repeat at the other two locations, illustrating the features of the local igneous rocks 

• POST THE FOUR PICTURES IN YOUR LOG TO SUPPORT YOUR FIND. (NOTHING NEEDS TO BE MESSAGED OR EMAILED)
• IF YOU ARE USING THE GEOCACHING APP. YOU WILL HAVE DIFFICULTY UPLOADING MULTIPLE PHOTOS - SUGGEST USING THE WEBSITE
• MAKE SURE YOUR PICTURES - [A] Identify a building, AND THEN to complete the main objective - (B) Get a little closer to ILLUSTRATE DIFFERENT CHARACTERISTICS of the rocks you see in your 'quadrat' (see hint)

EXAMPLE

The idea is that you focus in  on the a small area of the rock and illustrate the nature of the rock in a photo.

You need to use your "quadrat" like this, for your photos. It is essentially a "viewing window".

In the picture below you can clearly see crystals of three minerals (IGNEOUS ROCK)

AND THIS IN PICTURE -  you can clearly see clasts and a matrix (SEDIMENTARY ROCK)

LOCATION ONE

OLD SOUTH CHURCH

This building is actually the “new” Old South Church, constructed in 1875. 

The building blocks of this church are Roxbury Conglomerate, Boston’s most famous rock -  "Puddingstone". This Roxbury Conglomerate is from the Boston Basin, now generally considered a late Precambrian Avalonian structure. The conglomerate used in this structure is well indurated and has weathered well.

Two contrasting sandstones are used extensively as trim on the Old South Church. The reddish sandstone is likely the Longmeadow sandstone from the Connecticut Valley. The red arkosic sandstone was quarried at East Longmeadow, Massachusetts.

LOCATION 2

BOSTON PUBLIC LIBRARY.

The Boston Public Library consists of two wings occupying the block between Exeter Street and Dartmouth Street.

The granite on both the old and new portions of the library is the Milford Granite, a pink, foliated Precambrian biotite granite quarried at Milford, Massachusetts. In the old wing, the granite is used in load-bearing walls with rusticated rock-pitch surfaces. In the new wing, the granite has a thermal finish and is at least 2 inches thick. Massive monolithic slabs are used to form a distinctive wall around the new wing at street level.

The color and texture of the granite are quite distinctive.

Cross Dartmouth Street and the plaza at Copley Square to Trinity Church.

LOCATION 3

TRINITY CHURCH.

The stone on the exterior of the church is light colored granite liberally trimmed with brownstone. The granite is Dedham Granite and the trim is Longmeadow sandstone.

Generally coarser grained than the stone visible at street level, were used for the granite piers. Dedham granite, pale pink with green epidote specks, is known geologically as the late Precambrian Dedham granodiorite.

The fine grained pinkish grey granite on the exterior of the church might be Westerly Granite from Rhode Island. Westerly Granite is fine grained biotite granite noted for its uniformity.

Since the church is constructed on fill in the former Back Bay, the building is supported by 4,500 wooden piles, of which over 2,000 are in an area of 90 feet by 90 feet to support the foundation of the front tower.

Four granite pyramids, each measuring 35 feet square at the base, 17 feet high, and 7 feet square at the top sit on the piles for the tower. The wood piles must be kept saturated, and the water table under the church is constantly monitored.

From the guidelines,

You do not need to wait for permission to log your EarthCache. Requiring someone to wait is not supported by the EarthCache guidelines.

Log your EarthCache with the four required photos. We will review your log. If there is a problem, we will contact you to resolve it. If there is no problem, then your log simply stands."

☆  However you need to fully complete the logging requirements.