53 Trip A-3 KIMBERLITIC ROCKS OF CENTRAL NEW YORK DAVID G. BAILEY Department of Geosciences, Hamilton College, Clinton, NY 13323 e-mail: dbailey@hamilton.edu MARIAN LUPULESCU New York State Geological Survey, Albany, NY e-mail: mlupules@mail.nysed.gov INTRODUCTION The term “kimberlite” was first formally used to refer to the diamond-bearing mica peridotites of South Africa by Henry Lewis in 1887 at a meeting of the British Association for the Advancement of Science (Lewis,1888; Mitchell, 1986). Interestingly, similar mica peridotites were first discovered in upstate New York fifty years earlier. In his first annual report on the geology of the third district of New York, Lardner Vanuxem reported the presence of “serpentine” veins cutting through the Paleozoic sediments on the banks of East Canada Creek (approximately 10km east of the city of Little Falls) (Vanuxem, 1837). In his final geological report for the Third District, Vanuxem (1842) described four dikes of uncommon igneous rocks in a ravine east of Ludlowville (Tompkins County), the dikes on East Canada Creek (Herkimer/Montgomery County), as well as a “serpentine body” in the city of Syracuse (Onondaga County). According to Williams (1887a,b), the Syracuse serpentinite was discovered in 1837 by Oren Root who brought the rock to the attention of Vanuxem. Thus, 1837 appears to be the year when kimberlitic rocks were first observed and described anywhere in the world. The New York dikes are part of a larger north-south belt of kimberlitic intrusions on the western flank of the Appalachian mountain belt that extends from Tennessee to Quebec. These dikes are of particular interest to North American geologists because they provide the only direct information on the nature of the mantle and lower crust in the Appalachian interior, and they are the only expressions of Mesozoic magmatism in the region. Their age, origin, and relationship to plate tectonic processes are still poorly known or understood. DISTRIBUTION OF DIKES To date more than 80 distinct kimberlitic dikes and irregular intrusive bodies have been found in New York (Table 1). Most exist in clusters within an elongate NNE – SSW area between Syracuse and Ithaca, with the vast majority in ravines that feed into Cayuga Lake from the east, south, and west (Figure 1). Two somewhat isolated dikes in the Ithaca area are one at Filmore Glen State Park, and the other in a small quarry northwest of Ithaca (McDougal Rd dike) (Figure 2). The Ogdensburg (Eel Weir) dike in St. Lawrence County is the northernmost and most isolated dike in the state (Newland, 1931). Unfortunately, this dike is no longer exposed