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

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.

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.

Featuring “plutonic” (deep-Earth-formed) igneous rocks

The realm of Pluto, The Greek god of Hell, is one hot place, deep GCC Central Rock Park Section What rocks would form there? Certainly they would be molten and, being deep in the Earth, would cool slowly allowing minerals to form rather large sizes. Many common rocks form in this manner, for example, granite. The heat and pressure colliding tectonic plates during the Paleozoic Era melted a lot of pre-existing rocks which then cooled slowly into a variety of granite types. Rocks that did not melt became changed into metamorphic types. This section represents rocks melted or metamorphosed due to the Paleozoic assembling of Pangea.

#1 Stone bench, composed of granite curbing, quarry location unknown. Besides the gray granite, note the intrusions of coarse-grained material, called “pegmatite”. These represent minerals from the final stages of cooling of the magma chamber and have large sizes.

#2 Two polished granite pieces, discards from central Vermont’s monument industry. One sample is a pink, due to pink feldspar.

#3 Granite Porphyry samples (2), Kinsman Granite, Devonian Period, glacial erratics from Winchester, NH where this rock type occurs (Ashuelot Pluton). The large crystals of feldspar formed early in the crystalization of this sample, and were able to grow to large sizes. This is the defining feature of a “porphyry”. The large crystals are called “phenocrysts “.

#4 Granite Porphyry, Coys Hill Pluton, Worcester County, Devonian. This granite porphyry sample has been slightly metamorphosed — the fabric of the rock is changed from the usual granite pattern of randomness. Crystals of feldspar form the “phenocrysts”.

#5 Granite (pink) intrusion into gneiss. Original location unknown, from construction co. in Orange.

#6 Granite (tonalite or quartz diorite subtype), Hatfield Pluton, Hatfield, MA, Devonian age. Note intrusions of quartz with minor fluorite (purple).

#7 “Big Peg”, central sample. Goshen formation, Devonian Period, Goshen, MA. This large sample is an excellent example of an intrusion. The Goshen Stone (a mica schist with small garnets — also see sample #11 in the North Park area) has been intruded by pegmatite, a coarse-grained granite. When the sample was delivered, it broke. The pegmatite pieces 9a and 9b were formerly attached to “Big Peg”.

#8 Pegmatite intruding gneiss. This large sample came from a construction company site in Orange. It is probably the Monson Gneiss, a late Ordovician Period metamorphosed granite rock.

#9 Pegmatite samples, Devonian age, from Gilsum, NH and Goshen, MA Pegmatites are dominated by the common rock-forming minerals quartz, feldspar, and muscovite mica, but interesting accessory minerals can often be found. This is because at the final stages of cooling of a magma chamber, the atoms that didn’t fit into previous minerals, will be concentrated. In this group of samples, look for long black crystals of tourmaline and (in sample 9a) green apatite.

Unnumbered: smaller samples against brick wall. These samples represent several things: (1) Graphic Granite, Devonian Period, Gilsum, NH. The quartz and feldspar intergrow to form this unusual rock. (2) Vein Quartz, West Northfield and other locations. Quartz is a common intrusion (vein) because it is one of the first minerals to melt during metamorphic heating, and also the last to crystallize during magma cooling. So, many times, there is a lot of quartz that’s able to move through the rocks and crystallize in veins. Sometimes you can see the crystal points, but usually the quartz completely fills the vein opening. (3) Calcite veins, West Northfield. Groundwater fluids rich in calcium carbonate will deposit calcite in veins.

Calcite has cleavages and is softer than glass, so it can easily be differentiated from quartz, if you know what to look for. Do you?

Featuring extrusive igneous rocks (lava flows of basalt) from the Cheapside Quarry, East Deerfield, MA

The Connecticut Valley is famous for the dinosaur footprints and sedimentary rocks that were preserved in this “rift” valley, formed by the splitting of Pangea, the Paleozoic-age “supercontinent” that split drifted apart. As dinosaurs walked in the old Valley’s mud and sand, lava came to the surface and flowed across the valley. Today, these resistant “basalts” form the ridges of the Holyoke Range and much of the Pocumtuck Range in Greenfield and Deerfield.

Almost all these specimens are from Cheapside Quarry, east Deerfield, with a few pillows from other locations in the same basalt formation. They are from the early Jurassic Deerfield Basalt, dated at 194,000,000 years ago by the potassium – argon method.

#1 Lava Flow Bottom — a complicated mixture of basalt and hydrothermal altered material. There are two big and two smaller samples here (1a – 1d). The base of the Deerfield flow is sometimes mineralized by hydrothermal (hot, mineral-rich) fluids that deposit either micro-crystalline quartz or calcite material, and both look very similar until tested for hardness or reactivity to HCl acid (quartz is much harder & resistant to acid dissolution).
#1a – The basalt is dark colored while the mineralized areas (calcite in these samples) is brown.
#1b – The basalt fragments have been altered to a green color.
#1c – This interesting rock has a fossil plant stem (now turned to coal). The lava must have covered the plant, which was probably in wet soil which prevented burning (fragile, do not scratch the coal).
#1d – This flow bottom shows bubbles filled with sand that pushed up into the flow as it moved over wet ground.

#2 Pillow Lava “toes”. There is one big toe and many smaller samples along the wall that represent the outer edges of lava pillows. Pillows are tube shapes that only occur when lava flows under water. Our Jurassic basalt sometimes flowed into shallow lakes.

#3 Pahoehoe (smooth or ropey lava) Flow Top. Note how the bubbles (vesicles) converge at the top of this specimen, and that the top is a rather smooth surface. This represents a pahoehoe lava flow top, as opposed to aa, which is very rough and jagged.

#4 Columnar Basalt, 2 large specimens, central area. The smaller of the two weighed in at 2,250 lbs. The columns are due to shrinkage cracks developed as the lava cools.

#5 Glacial scratched basalt surface. The over-riding glacier commonly scratches rocks. See if you can pick out the dominant flow direction, a secondary flow direction, and some bulldozer scratches. On one of the vertical sides are fault scratches, called slickensides.

#6 Slickensides. Many earthquakes occurred along faults in the valley as Pangea split. The frictional heat and motion of one side against the other, partially melted and scratched the surface of the fault, and that’s what is preserved here! Sometimes minerals filled in and around the broken sections, too.

#7 Breccias, several samples with striking angular patterns with mineralized veins. These are very unusual specimens. The lava has been obviously cracked and mineralized. There are two possible scenarios: earthquakes (faulting) or volcanic explosions could fracture the rock. The Deerfield breccias are probably due to steam explosions that blasted through the basalt creating the zones of broken rock. Groundwater and hydrothermal fluids passing through the cracks would then bring in minerals that would precipitate in the open spaces. The mineralization consists mainly of calcite.