Cusiiing — Geom)GY of Clinton County. 



monchiquites, fourchites and camptonites to the later period; though <m 

 account of the facility with which the diabases and camptonites shade into 

 one another, it may not always be possible to determine to which of the two 

 a given dike in the Pre-Cambrian rocks should be referred. 



The diabase dikes are very common and widespread. Scarcely an out- 

 crop of any extent of the Pre-Cambrian rocks can be found without disclosing 

 the presence of one or more of them. But, as was to be expected, their 

 distribution is irregular, as they are only occasional in certain areas, whereas 

 others are fairly seamed with them. Sometimes a veritable plexus of dikes is 

 exhibited, anastomosing in all directions, enclosing great horses of the country 

 rock, and so variable from place to place that no satisfactory generalized 

 measurements can be made. The most notable example in the county is in 

 southeastern Altona township, where the Old Military road crosses the north- 

 east spur of Rand's hill. Cutting the gabbro here is a grand exhibition of 

 dikes, which will be more fully described under the discussion of that town- 

 ship.* Another striking exhibition of dikes is found along the west shore of 

 Upper Chateaugay lake, and yet another on Dannemora mountain. 



Appended is a tabulated list of the dikes found in the county by the 

 writer. Kemp has noted the occurrence of others in the Lyon mountain iron 

 mines, and two from Palmer hill, and three others have been described 

 by "Eakle. 



* See E. Emmons. Natural History of New York, Geology, Part 11., p. 28. 



