244 



A. S. PACKARD, Jr., ON THE GLACIAL PHENOMENA 



A section given in the ascending order, shows the follow- 

 ing succession of beds and their characteristic fossils : — 



1. A few feet of unfossiliferous gravel resting directly 

 upon the gneiss rock. 



2. A few inches of a sandy grit, which weathers into 

 an exceedingly hard sandstone, rich in life, containing 

 Memhranipora americana, Lepralia variolosa, Pecten islandt 

 cus, Pandorina arenosa, Astarte Banksii, A. elliplica, Serripes 

 gronlandicus, Natica clausa, Fusus toriiatus, Buccinum grdnlandi- 

 cum. Similar gritty sands are found in patches in the clays 



I. leal Section of Quaternary formation at Gardi- a "OVe. 



ner - Maine - 3. A soft black clay with a strong odor of marsh mud 



containing shells and the remains of Alga?. 



4. These beds gradually pass into what the brick-makers call " bar clay." It is about 

 seventy-five feet thick and is very finely laminated, very evenly bedded, consisting of lay- 

 ers an inch thick, separated by thin lamina? of a pure silicious sand. It also contains a 

 few polished and scratched gneiss and greenstone boulders scattered through its mass. 

 Here nearly all the fossils mentioned in the accompanying list occur. 



The lowest bed of gravel I did not myself see, but it was°described to me by the former 

 proprietor of a pottery manufactory, as resting directly upon the solid rock, as it is often 

 penetrated in boring for wells, and is thus found to be absent in many places about the 

 town, as very frequently the rock is reached directly after digging through the black mud 

 or clay. Most of the wells, after being sunk twenty-five feet, terminate in 'this soft clay and 

 the water is unfit for use ; while very deep wells, sometimes sunk seventy-five to one 'hun- 

 dred feet down into the stratum of clean pure gravel, afford the purest water 



The gritty beds near the bottom of the series of clay strata contain deeper sea forms 

 than those above, and the paleontological evidence leads to the conclusion that they 

 formed a sandy, shelly bottom like our submarine banks, swept by comparatively swift 

 ocean currents ; that at a later period the currents were not so strong; that the sea bottom 

 changed into the floor of a deep bay or estuary, in which river silt accumulated where the 

 most delicate shells lived, and the Natica deposited its eggs in broad, thin, platter-like 

 masses, and littoral shells, such as Mya and Mytilus, abounded. Again, the waters growing 

 fresher, more river sand took the place of mud, the shells disappeared from the loamy strata 

 and then came an era of denudation, and the deposit of the sea shingle and beach sand! 

 which filled up the hollows and inequalities of the boulder clay. 



Returning again to the fossiliferous clays, they were found sparingly stocked with boulders 

 of gneiss and argillaceous slate, often highly polished, with shells firmly adhering to them 

 as if pressed upon them, since they were flattened out, broken and cracked All these 

 c ays like those everywhere observed in Maine, where weathered, present a rude and un- 

 stratified steep cliff with a slight talus of stones at the bottom. The shells most character- 

 istic of this deposit were Nucula antiqua and the two species of Astarte, Mya armaria, and 

 Myhlus eduhs Owing to the pressure of the superincumbent strata, many of the shells es- 

 pecially the Nucula were greatly flattened, and distorted into a variety of forms very differ- 

 ent from the natural shape, reminding us of the distorted shells of the paleozoic rocks Sev- 

 eral forms, if presented to one unacquainted with this fact of distortion, would be readily mis- 

 taken for distinct species, as they are often elongated without being flattened, or cracked 



