THE EXCURSIONS. 6 



to members of the American Association for the Advancement of Science and to all 

 other persons who desire to take advantage of them, without charge excepting the 

 expenses of subsistence and transportation. A circular giving an itinerary and 

 mention of the various points or objects of interest which it was proposed to visit, 

 with lists of geological writings bearing upon those features, had been widely dis- 

 tributed. 



The excursion in stratigraphy and paleontology planned to include central and 

 western New York, under the conductorship of Professor Charles S. Prosser, and 

 that in the economic geology of western New York, under Dr F. J. H. Merrill, had 

 been abandoned at the last on account of lack of sufficient interest. 



The excursions in petrographic geology, under the guidance of Professors J. F. 

 Kemp and Charles H. Smyth, Jr., and in Pleistocene geology, under the guidance 

 of the Secretary and Mr G. K. Gilbert, were carried out successfully. It had been 

 expected that Mr Frank Leverett would assist in the latter excursion, but he was 

 prevented by illness. 



Professors W. N. Rice and C. H. Hitchcock were called upon to give 

 an account of the work of the petrographic excursion. They spoke as 

 follows : 



REMARKS ON THE PETROGRAPHIC EXCURSION 

 BY W. N. RICE AND C. H. HITCHCOCK 



Professor W. N. Rice spoke as follows : 



The party assembled at Port Henry, on lake Champlain, on Monday, October 

 17, and the first three days of the week were devoted to the study of the eastern 

 part of the Adirondack region, under the guidance of Professor J. F. Kemp. 



Monday forenoon was spent in the study of the crystalline limestones, gabbros 

 and gneisses north of the town and near the lake shore. Special attention was 

 called to the gneissoid modifications of the gabbro, the transition being shown 

 from a typical massive gabbro to a rock which is essentially a hornblende gneiss. 

 The contacts between the gabbro and the limestone formed another feature of 

 special interest. Tongues of gabbro were seen projecting into the limestone, some- 

 times apparently isolated from the main body of the gabbro. The phenomena 

 would seem to indicate intense dynamic action subsequent to the consolidation of 

 the gabbro. While some of the bands of dark silicates enclosed in the limestones 

 appear to be pretty certainly extensions of the gabbro, others may be thin strata 

 of schist resulting from the metamorphism of silicious sediments which were origi- 

 nally interstratitied with the limestones. 



Monday afternoon the party visited the great magnetite mines at Mineville, and 

 the complex stratigraphic relations of the ore bodies were explained by Professor 

 Kemp. The ore occurs on the contact between underlying sheets of gabbro, often 

 metamorphosed to hornblende gneiss, and an overlying quartzose gneiss. Asso- 

 ciated with the magnetite at Mineville, are veins of an oligoclase pegmatite con- 

 taining beautiful crystals of zircon, of which numerous specimens were obtained. 



Tuesday the party embarked in a steam-launch, intending to cruise along the 

 lake shore to Plattsburg, and study as many of the dikes and other interesting 



