62 NEW YORK STATE MUSEUM 



The igneous rocks, where homogeneous and free from Grenville 

 inclusions, without exception form the highest mountain masses. 

 Occasionally the gabbro bosses appear to be slightly more resistant 

 than the country rock and they then form the tops of low mountains 

 or hills. 



Another topographic feature often locally conspicuous is the 

 sand flat or flat-topped sand terrace. Among the best examples 

 are : in the vicinity of Warrensburg and Pottersville, west of Star- 

 buckville, southwest of North Creek, and at a number of places 

 southwest of Johnsburg. These represent delta deposits which 

 were formed in glacial lakes which will be described in the suc- 

 ceeding pages. 



RELATION OF TOPOGRAPHY TO ROCK STRUCTURES 



Some of the most prominent topographic features of the quad- 

 rangle are the bold escarpments, more or less well-defined ridges, 

 and isolated mountain masses or domes of igneous rock. These 

 rock domes will be especially treated under the next heading. 

 Most of the escarpments or ridges are due to faulting and have 

 already been described. Some ridges, however, especially those in 

 the Grenville areas, are due to other structural features combined 

 with rock character. Thus the prominent ridge of gneiss which 

 runs several miles southeastward from North Creek is due to the 

 fact that a belt of weak limestone everywhere dips sharply under 

 the harder rock of the ridge. The ridge south of Valentine pond 

 is to be explained in a similar manner. Many small streams in the 

 Grenville have developed along structural belts of weakness. 



In the igneous rocks, too, there is a notable tendency for local 

 short ridges and valleys to develop along lines parallel to the direc- 

 tion of foliation. 



The most remarkable topographic feature in the whole region 

 is the deep, narrow rift between Crane and Huckleberry moun- 

 tains, which is certainly due to a combination of faulting, a belt of 

 weak Grenville, and some erosion since the faulting. 



EXFOLIATION DOMES ^ 



One of the most striking features of the landscape, especially 

 in the southern two-thirds of the quadrangle, is the prevalence of 

 distinct, isolated, domelike, topographic forms which rise hundreds 



^ For a fuller discussion of this subject, see paper by the writer in N. Y. 

 State Mus. Bui. 149, p. 187-94. 



