REPORT OF THE DIRECTOR I916 .I59 



in the ^Yeak Trenton beds near the Haven Bay fault. This ancient 

 lake shelf is fairly well shown near the right edge of figure 2. Note 

 that the present surface does not follow the slope of the bedding 

 planes but cuts across their upturned edges. The strand line was 

 then farther inland than now. When the lake was reduced to its 

 present level it had to start near the outer point of the Chazy 

 bluff and begin, anew^ its carving of the Trenton. 



In New York State Museum Bulletin 133, pages 159-63, will 

 be found an article by the author dealing with evidence of a pre- 

 glacial lake which he has named Lake Valcour. A still more 

 ancient body of water worked long enough to cut the Trenton and 

 other weak beds of the region down to a rather extensive local 

 plane but it did not succeed in removing the harder Chazy mass 

 now forming Bluff Point. The ice sheets of the glacial periods 

 next began their grindings of Clinton county surfaces but they 

 succeeded only in lowering Bluff* Point from its more ancient 

 domineering height and in rounding off its edges. These ice 

 scourings, however, grooved the old wave-cut Trenton shelf and 

 spoiled its flatness. This flatness the Hochelagan sea tried to 

 restore by cutting down the hills of glacial deposits and using the 

 removed material to fill up the hollows. Last of all a new brook 

 system, draining into Lake Champlain, began to carve the region, 

 but so far it has cut only rather narrow channels in the late sea 

 bed. The general level of the country, which we first noticed, is 

 due then to a sequence of causes involving ancient seas, glacial 

 periods, and recent seas, all of which left traces of their work. 



At different times during this elevated interval the rocks were 

 in places cracked open to great depths, and these cracks were filled 

 with molten lava. Two of these lava-filled fissures are to be seen 

 at Cliff Haven. One of them is near the southern boundary of the 

 Champlain Assembly grounds and is best seen from a boat. The 

 lava filling this fissure proves, on analysis, to be like that first dis- 

 covered by Bonet in the Monchique mountains of Portugal and is 

 now known as Monchiquite. At another period in the history of 

 this region the assembly grounds were again fissured, and this 

 fissure filled with a very different lava called fourchite (from 

 Fourche mountain, near Little Rock, Ark., where similar dikes are 

 found). This fourchite is the only known dike of its kind in 

 Clinton county and may be seen just north of the steamboat land- 

 ing. It is 32 inches wide and runs about N. 95° W. or toward the 

 extreme southern end of Crab island where a few displaced masses 

 of it are still to be seen. This dike is also of unusual interest 



