Rock Park: Northern Section

Featuring armored mud balls in conglomerate plus other sedimentary rocks as well as metamorphic samples

Professor Richard Little with an armored mud ball

Samples numbered 1-6 comprise the rare Armored Mud Ball Collection. Nos. 1 – 5 are from the early Jurassic Turners Falls Sandstone formation, quarried rocks from Turners Falls, removed from the old Red Bridge cable anchor at Unity Park . Sample GCC North Rock Park Section 6 is from late Triassic Sugarloaf formation (“Falls River” beds), Cheapside Quarry, east Deerfield.

The armored mud balls (1-5) are in conglomerate rocks that were removed from the southern suspension cable anchor of the old “Red Bridge” that spanned the Connecticut River from Unity Park, Turners Falls, to Riverside in Gill from 1878 – 1938. It’s interesting to note that armored mud balls are extremely rare in the geologic record, yet here in Franklin County we have samples from two different formations. Armored mud balls have not been found in other parts of the Connecticut Valley, and are noted from only about 10 places in the whole world.


How do armored mud balls form? Hard mud falls into a stream and as it tumbles downstream it becomes round and soft and sticky on the outer rim, which then picks up pebbles (the “armor”) from the stream bed. The armored balls are then buried and gradually “lithified” (turned to stone). All other sites of armored mud balls are from beach deposits where waves caused the rolling and armoring. The Franklin County armored mud balls are the only stream-formed armored mud balls in the world!

#8 An unusual Sedimentary Breccia, early Jurassic Turners Falls Sandstone formation, Barton Cove, Gill, MA. This sample’s origin was quite dramatic. Note the highly angular nature of the components (angular fragment-rocks are called “breccia” meaning “broken”). Whenever rock fragments are large and angular, it indicates a very energetic process — landslides, faulting, stream floods, etc. What caused these fragments? While the origin of this strange rock has been debated, most geologists now believe that it is due to faulting. The quake shake and fault movement fractured these sedimentary layers to create the jumble seen here.

#7 & #9 Sandstone (variety: arkose), Turners Falls Sandstone

Can you find: mud cracks, raindrops, and bedding laminations?


# 10 Mud Cracks, Ordovician Period, Manlius formation (limestone), town of New Salem, (eastern) New York. More evidence of warm shallow sea conditions from 400 million years ago, long before the rocks of the Connecticut Valley formed, and several millions of years older than the fossils specimens lying in front, described next.

Samples near #10

Small Samples near 10: Marine Fossils, Helderberg Mountains, eastern New York. Look for pencil-sized coral colonies, larger “horn”corals, and a few larger coral “heads”, plus small colonies of branching bryozoans, clam-like brachiopod shells, and many crinoid stems (sometimes seen in cross section: little “tires” about 1/10 of an inch across. These samples are from various formations that were formed under shallow ocean conditions during the early Paleozoic (Ordovician to early Devonian Periods). At this time eastern North America was located in the warm tropics south of the equator. Similar rocks in western Massachusetts have been metamorphosed by continental collisions to become beautiful white marble (sample 18). Impure marbles are also common and look dull brown to gray but may weather into strange shapes such as the “anvil stone”, sample 15.

Metamorphic Rocks: formed by the alteration of pre-existing rocks by heat, pressure, and chemically-active fluids. All these rocks were squeezed by the continental collisions that occurred as the supercontinent of Pangea was assembled and the Appalachians were built during the Paleozoic Era.

#11 “Goshen Stone” Goshen formation, Devonian Period. We are fortunate to have some excellent exposures and quarries in this mica schist rock which features garnets of various sizes. This rock represents the metamorphism of muddy sediment from deeper ocean conditions. The “post” is cut from Goshen stone. Note the regular layers which must represent some original bedding of the sediments (due to seasonal events?) before metamorphism.


#12 Mica schist with hornblende, Hawley formation, Ordovician Period. This beautiful stone is marketed as “Crystal Crowsfoot” by the Ashfield Stone Co. Hornblende “bowties” are prominent and form as crystals grow during the heat & pressure of metamorphism from a common center. The Hawley formation is interpreted as being part of a volcanic island arc created by an easterly-dipping subduction zone prior to the late OrdovicianTaconic Orogeny.

#13 Mica schist with prominent garnets. Rowe, MA

#14 Mica schist with prominent garnets. Northfield, MA Devonian Period, Littleton formation

#15 Anvil stone, location unknown, western MA. An impure marble weathers to form the “hollow”, harder schist forms the rim.

#16 Gneiss, Monson Gneiss, Palmer, MA.

#17 Schist with prominent fold. Glacial erratic from SW NH.


#18 Stockbridge Marble, Cambrian Period, from Lee, MA. and some smaller samples from the Proctor, VT area. This beautiful large white rock is metamorphic limestone, a rock rich in CaCO3 from limy mud and shells from a warm shallow sea. At this time western Massachusetts was south of the equator. Rocks from this region in western Massachusetts are commonly crushed for ornamental stone, to make cement, or even antacid tablets (“Tums”).


#19 Quartzite Samples. These samples, all glacial erratics from the central Berkshires of MA, probably represent the Cheshire Quartzite, a Cambrian Period beach and shallow water quartz sand deposit, now metamorphosed to quartzite.

Miscellaneous samples on the western rim, by the “uphill” seat: dinoprint, coal fossil, and a grinding wheel from the Russell Cutlery Co ruins next to the power canal, Turners Falls, found during the construction of the coal-fired power plant. This is an interesting piece since it is not a Connecticut Valley sandstone, perhaps coming from older sandstones of the Hudson Valley.

Northern Section Central Section Southern Section