FOURTH REPORT OF THE DIRECTOR I907 1 5 



beds. Only one of these has commonly been recognized by other 

 investigators. At Cystid point a reef is shown and its extinction 

 and the deposit of sediment over it is clearly to be seen. Five 

 meters down from this horizon and 300 meters to the north is 

 another. Twenty-three meters down and 1000 meters to the north 

 comes the more massive one which forms the " dove color " of 

 Tiger point. Reef material is found again from 400 to 500 meters 

 north of this and at a horizon 70 meters below the surface at 

 Cystid point. This reef is as large as the Tiger point reef and 

 in many respects resembles it. The shore is of a deeper blue dove 

 color on the whole, yet this darker dove color may also be found in 

 the Tiger point reef. The rock abounds in cephalopods and the 

 trilobite Glaphurus pustulosus. The rocks of Sloop 

 island (which show a pure dove colored rock as light as that of 

 Tiger point) seem by their position to belong to this reef. One of 

 the reefs noted belongs to the upper Chazy, the other 47 meters 

 below it, is in the middle Chazy. 



The fault system of the region is of interest and corrections have 

 been made of the location of the faults mapped by others and also 

 data on new faults acquired. A preliminary map of the intricate 

 fault system of the Plattsburg region has been made and the fact 

 brought forward that the form of Lake Champlain is the outward 

 expression of some of the more extended of these faults. Enough 

 evidence has been acquired to show the presence of two widely 

 different systems and that correlation of the scattered observations 

 is at least in part, possible. The north and south system appears 

 to be the younger, or at least has suffered the most recent additions 

 to its displacements. 



A number of interesting observations have been made on the 

 island, bearing on the glacial history of the region and on the 

 striae of the glacial lx)ulders. An enormous amount of the energy 

 of a moving glacial sheet is spent in reducing its ground moraine 

 to powder. The sheet of till in actual contact with the bed rock 

 does not move so rapidly as the sheets lying over this. As a conse- 

 quence comparatively few stones of the till are found with surfaces 

 ground by contact with bed rock, for such a grinding produces a 

 flat face with hundreds of parallel lines as may be seen in the adjoin- 

 ing photograph ; on the contrary curved outlines predominate caused 

 by contact with each other. 



Highlands of the Hudson. Geological fieldwork in the High- 

 lands was continued by Dr Charles P. Berkey during a part of the 



