102 



laid down by the melting of the ice among masses of the country 

 rock of granite and gneiss. On this limestone boulder, about 

 five feet long and three feet thick is a thriving colony of the 

 Walking Fern, the only one known in the Harriman Park, or 

 the Hudson Highlands, though perhaps similar limestone erra- 

 tics not yet reported, in remote spots, might bear like colonies. 

 The marvel is, how the spores of the fern brought from the \\'all- 

 kill \'alley, where it is common on the country limestone, took 

 root upon this isolated boulder among the Highland Archaean 

 formations. 



On July 28, another stand of Walking Fern was seen, on 

 Firey Brook, a stream which enters Pompton Lake, near Pomp- 

 ton, X. J., on its east side, a quarter of a mile above the out- 

 let dam. The left fork of this brook has worn a pretty gorge 

 with a wall fifty feet high on the south or cutting side of the 

 stream, with Xewark sandstone at the top and at the bottom 

 a curious kind of conglomerate, with pebbles and cobbles of 

 rounded or sub-angular limestone, of basalt similar to that in 

 the Packanack Ridge, close by, and of the Xewark sandstone, 

 just abo\-e. This conglomerate has been described by Dr. 

 H. B. Kummel, in his report on the Glacial Geology of Xew 

 Jersey, but is probably much older than the Pleistocene. The 

 source of the sandstone and of the basalt is ob^'ious enough, as 

 these formations are in place close by, the igneous rock being 

 visible in the dam at the outlet of the lake, and making up the 

 semi-circle of hills which surrounds the brook ^■alley, while 

 the sandstone is the pre^'ailing formation in the Pompton 

 Valley to the west and in Bergen County to the north, and there 

 is an inlier of it in the lower courses of both branches of the 

 brook, underlaid b}' the conglomerate. 



But the source of the limestone is not so obvious. It is 

 thought to be of the same formation as that quarried on the 

 surface at Tomkins Cove, and also found on the east side of 

 the Hudson on Verplanck's Point. Dr. Kummel thinks it 

 existed in the form of ledges or cliffs along the front of the older, 

 Archaean formation of the Ramapo mountains, and that most 

 of it was carried down some thousands of feet by the great 

 fault — the famous Logan Line — which bounds the Ramapo 

 granites and gneisses and the Triassic sandstones and diabases 

 or basalts in Rockland County, Xew York and Bergen and 

 Passaic counties in X^ew Jersey. But, before this faulting, 



