REPORT OF THE DIRECTOR I916 147 



ride over the upper surface of the intrusive. The relations are 

 interesting in that they give a clue probably to the extreme contor- 

 tion and flowage effects exhibited by the succeeding photographs 

 which are taken a little farther north in a second exposure of the 

 limestone. The gabbro forms only a small boss and is succeeded by 

 syenite gneiss in which occurs a band of limestone that forms the 

 shore line for nearly a mile. It is in this area that the freshest 

 faces of limestone are found. 



The deformation that is revealed in the pictures is ,no doubt 

 the result of squeezing between the more resistent igneous rocks 

 which themselves have assumed more or less cataclastic and 

 gneissic characters under the strain. The effects could only have 

 been accomplished under conditions of cubic compression such as 

 would be supplied by a thrust exerted upon the beds when they 

 were heavily loaded or weighted down by many thousands of feet 

 of cover. 



The nature of the silicate bands in the limestone is something 

 of a problem, as is remarked in the citation from Professor Kemp's 

 bulletin. It is not unlikely that some of the bands are dikes 

 derived from the gabbro and syenite magmas, as instanced by the 

 dark amphibolite bands which in appearance and mineral character 

 are scarcely distinguishable from the border phases of the basic 

 intrusions. This type is illustrated by plate 2 in which is seen 

 a small band of black amphibolite that has been folded and broken 

 up under the pressure transmitted by the mobile limestone, itself 

 giving no evidence of the deformation that has taken place. In 

 plates 4 and 5 the bands are in part of a more siliceous character, 

 and may well represent original impure layers in the beds. 



Plastic deformation of the Grenville limestones is a common con- 

 dition throughout the Adirondacks, if one may base an inference 

 upon the circumstance that it is the purer beds alone that do not 

 reveal its effects; in them the results would be masked even if 

 present. 



