602 WILLIAM J. MILLER 



expect a general northeast-southwest strike of both rock masses and 

 foliation of Grenville and intrusives to be of common occurrence. 



A statement made by Smyth twenty years ago regarding black 

 gneiss inclusions in the syenite-granite series of St. Lawrence 

 County is significant in this connection: "The parallel arrangement 

 of the neighboring bands [inclusions] doubtless results from currents 

 in the molten magma, which would tend to produce such a result. 

 It is probable that the breaking into blocks resulted, in part, from 

 strains applied after the magma was in a pasty and partially crystal- 

 lized state. The blocks were more or less widely separated, and 

 the intervening space was tilled by the magma which flowed around 

 the blocks without destroying their angular contour, and. at the 

 same time, often produced an obscure flow structure in the gneiss 

 parallel to the sides of the inclusions." 1 The bandlike inclusions 

 here described by Smyth are seldom more than a few rods long. 

 but the writer believes the principles set forth are applicable on a 

 much larger scale throughout the Adirondack region. 



Such parallelism of structural features does not. therefore, 

 demonstrate that the rocks have been thoroughly compressed 

 subsequent to the syenite-granite intrusions. The northeast- 

 southwest structural features here referred to are more pronounced 

 in the Thousand Islands region than is usual throughout the Adiron- 

 dacks, and this may be readily explained by granting somewhat 

 greater lateral pressure during the intrusion in the tirst-named 

 region. In any case it is necessary to assume only very moderate 

 compression — far less than would have been necessary to elongate 

 the batholiths and develop distinct foliation in them after their 

 complete solidification. 



Exceptions to northeast-southwest structure. — There are many 

 exceptions to the general northeast-southwest structural arrange- 

 ment, and these prove that no severe tangential compression could 

 ever have been exerted throughout the region after or during the 

 intrusions. Among such exceptions are sharp variations in strike 

 of groups oi inclusions of well-foliated Grenville gneiss in the intru- 

 sives. Examples have already been cited. If the whole region 

 has been subjected to compression thoroughgoing enough to flatten 



1 C, H. Smyth, 15th Ann. Rep. New York State Geologist, 1805. P- 49 1 - 



