Crsm.\<; — GrEOLGGY OF ClFNTON COUNTY. 



537 



diallagic habit, both crammed full of intrusions. The interspaces are of 

 granular structure, containing plagioclase and some nnstriated feldspar, 

 neither with inclusions ; augite, also without inclusions, hypersthene, horn- 

 blende, biotite and magnetite. This granular portion has evidently not 

 resulted from the mere granulation of the original rock, but is almost wholly 

 due to recrystallization. Reaction rims of biotite and hornblende around 

 magnetite are excellently shown. Grarnet seems to be absent. Throughout 

 the county it is not so characteristic of the basic gabbros as of the 

 anorthosites, though frequently present in them. Aside from this exposure 

 no rocks of this series have been seen in the township. 



Series IV. A tongue of Potsdam sandstone runs into Dannemora, 

 occupying the depression between Dannemora and Ellenburgh mountains, 

 and traceable to Chazy lake, at the Chazy Lake House. Though hemmed in 

 between the gneisses, no coarse conglomerate lias been seen, and most of the 

 rock is the red, hematitic, easily decomposing arkose. The best exposures 

 are in Steep Bank brook, two miles north of Dannemora village, and here 

 at an altitude of 1,500 feet, the greatest elevation known to be reached by 

 this rock in the county. 



Series I. Forty-one dikes have been found in Dannemora township. 

 Kemp has noted eleven which cut the ore-body in the Chateaugay mine at 

 Lyon mountain, and five more have been described b\ Fakle from Upper 

 Chateaugay lake. The remainder have been found by the writer. Along the 

 west shore of Upper Chateaugay lake, and along the road north from 

 Dannemora over the mountain, are notable exhibitions of dikes. Four of 

 them are of bostonite, the rest are diabases. Only two of them need further 

 notice here. 



Dike No. 4C>, w est of the lower end of Chazy lake is of the bostonite 

 tvpe, but abnormal, it is dark brown to black in color, non-porphyritic, and 

 rathei' coarse for this rock, with the trachytic structure not well marked. It 

 is almost wholly made up of rather large orthoclases, which are packed full of 

 inclusions of green hornblende and biotite. The two minerals have precisely 

 the same color, so that in many cases it is impossible to distinguish them from 

 one another, but both are present. There are also some larger, irregularly 

 bounded green hornblendes which seem secondary after a nearly colorless 

 mpnoclinic pyroxene, two cores of which remain in the slide surrounded by 

 the hornblende, which is of the uralite type. It is a curious rock, and if 

 classed with the bostonites, must run very low in silica for that type. Just 

 what was its original condition, is not clear. 



