MARKINGS IN PENNSYLVANIAN SANDSTONES 77 
strand markings have the appearance of being made by roots or 
other portions of trees. 
3. Action of ground ice molding unconsolidated sandy clays.— 
Floating land ice has been shown by Lyell to be capable of furrowing 
consolidated sandstone Dr. Clarke and Professor Woodworth 
concur in the opinion that the markings in the Upper Devonian 
of New York are of similar origin. The occurrence described by 
Lyell was at Cape Blomidon, on the Bay of Fundy, where heavily 
“‘nacked”’ ice often 15 feet thick with fragments of amygdaloidal 
basalt frozen in the base, is pushed over ledges of Triassic sand- 
stone with the rise of the tide. 
Climatic conditions such that land and ground ice could be 
formed at various times during the deposition of 1,000 feet or 
more of sediments in the middle and upper Pennsylvanian are 
within the range of possibility and the faunas and floras would 
not necessarily prove or disprove such an assumption.? But if 
floating ice were present it should have gouged out the muds in 
some places and produced considerable lumps in others. Contrast 
the absence of such disturbances with Dr. Kindle’s description 
of the action of “‘ice-shoved bowlder or ice cake”’ in the Mackenzie 
River: . 
The plowing and gouging action of ice is nearly everywhere in evidence 
along the Mackenzie. At the head of the river, in the eastern shallow channel, 
one can see through the clear water numerous deep grooves made by ice 
cakes or bowlders pushed by ice in the bowlder clay of the bottom. In the 
gravel or slits of low islands the broad grooves made by ice-shoved bowlders 
or ice blocks can often be traced for a considerable distance. In some localities 
the plowing and scooping action of the ice carries quantities of mud from the 
bottom to the banks of the river.3 
A comparatively smooth surface on the bottom of the ice would 
produce the required parallel markings and might produce cross- 
markings, but not the irregular markings unless small cakes of 
* Travels in North America, Vol. II (1845), p. 144. 
2 “Tt seems possible to state that there is evidence for presuming that the Permian 
glacial period was preceded in the Carboniferous by a degree of cold permitting 
floating ice in continental bodies of water and also in the sea in middle latitudes.”— 
J. B. Woodworth, ‘‘Boulder Beds of the Caney Shales at Talahina, Oklahoma,” 
Bull. Geol. Soc. Amer., Vol. XXIII (1912), pp. 457-62; quotation p. 462. 
3 ““Notes on Sedimentation in the Mackenzie River Basin,” Jour. Geol., Vol. XX VI 
(1918), pp. 341-60; quotation p. 353. 
