BOTANICAL EVALUATION OF THE GOAT ISLAND COMPLEX, NIAGARA FALLS, NEW YORK
The Cascades are the long, parallel rock ridges perpendicular to the flow of the Niagara River between the brinks of the falls and the western margin of the Grass Island - Chippawa Pool, or the body of water between these ridges and the joining of the two channels of the Niagara River as they converge below Grand and Navy Islands. The Cascades are quite exposed in winter just above the east end of the Three Sisters. These ridges may have provided access to Goat Island before there were bridges, perhaps by entering the river (New York side) "two miles above, so as to reach the dead water occasioned by the Island dividing the River into two Currents. From the Island a bar stretches far up the River, which principally enables you to reach the Island, as you pole your canoe along this bar," Maude, 1826. Occasionally, according to Mr. Maude, "Mr. [Steadman] remembers having once seen the bed of the River dry from the Fort Schlosser [i.e. American] side to the bar running from the South point of Goat Island." The bar may have arisen by breaking the force of the current in the river by favorable elevations in the Cascade bedrock formations. It is conjectured that these generally north-south-oriented ridges are erosional features of a north-south trending river ancestral to the present Niagara River.
The calcareous, dolomitic bedrock of the islands provides a tough, resistant cap to softer strata below it. It is this resistance to weathering that produced the Niagara Escarpment, a north-facing, east-west trending feature extending through southern Ontario and central New York State. The present cataracts of Niagara had their origin falling over the precipice formed by this escarpment seven miles downriver at Lewiston, New York and Queenston, Ontario, and so the escarpment may be said to extend up the gorge of the Niagara River, decreasing in elevation as it proceeds south in conformity with the regional dip of rock strata in the region.
Dolomite has a characteristic structure due to fracturing. As the weight of the advancing and receding continental ice sheets formed during the regional glaciations of the Pleistocene, the local strata were alternately depressed and then elevated, creating a flexion in the more rigid layers, resulting in the characteristic blocky fracturing or jointing of limestone and dolomite strata. Off-loading of superficial strata and sediment by glacial scour also contributed to fracture of the remaining bedrock. Accelerated jointing in the immediate vicinity of the gorge and cataracts is due to stress on the bedrock lost by excavation due to erosion (Krajewski & Liberty, 1981). Rainwater tends to run down through these joints rapidly, creating a drier environment at its surface than other types of bedrock, such as sandstone and shale.
Dolomite has a great deal of the element calcium in it. Calcium is readily dissolved by acids. Rainwater is acidic and causes the great solution cavities formed in the native limestone of some of the more famous cave-formations in the United States, such as the Carlesbad Caverns of New Mexico, and the cavern-systems in West Virginia (Jones, 1973). Dolomite is limestone with the addition of magnesium, which makes it less easy to erode by solution than ordinary limestone (Krauskopf, 1967).
The texture of the Lockport Dolostone (actually the Goat Island Dolostone, type locality "Goat Island at the brink of Niagara Falls") is not uniform but "stylolites and carbonaceous partings are common. Vugs containing gypsum, sphalerite (zinc sulfide), and calcite are common in thin zones" (Kilgour & Liberty, 1981). Dissolution of these deposits leaves the surface of the bedrock in the area of the Three Sisters pocked and irregular with circular depressions. These little pits may serve as natural "flowerpots" for the colonization of plants on recently exposed river bed.
In falls over limestone bedrock, such as Sitting Bull Falls, New Mexico, the redeposition of limestone on surfaces exposed to the spray of the falls and flowing water is pronounced whereas at Niagara such deposition is not very visible, unless as a result of biological action (personal observation; see "didymodontoliths" in the moss section). Groundwater in the Lockport dolomite formation underlying the Goat Island complex may bring "a calcium sulfate or calcium bicarbonate water ... very hard and moderately mineralized. A highly mineralized water, characterized by higher concentrations of sodium and chloride than those measured in typical Lockport water, occurs in the lower two zones of the formation" (Johnston, 1964).
It appears that the water in the Niagara River, rather than rainwater, produces the most visible effects of dissolution in the joints of the dolomite caprock, if not because it is more acidic, then because of the added force of pressure. Joints become great fissures visible from the air (Krajewski & Liberty, 1981) and on the Three Sisters: the deep gap between Brother Island and the Third Sister, and the great fracture on the Second Sister, north-east end. These joints, pushed apart by hydrostatic pressure and widened from dissolution by river-water at the brinks of the cataracts contributes to the retreat of the gorge upriver together with the prior weakening by fracture of softer strata below (Krajewski & Liberty, 1981).