J. F. Kemp— Extension of the Cortlandt Series. 251 



reverse succession. The succession here noted is also in accord 

 with artificial experiment. 



Between the general diorite that forms the greater part of 

 the Rosetown area and the diorites and mica-diorites of the 

 main area, the writer can trace no mineralogical differences 

 worthy of note except those already given. Omitting the hy- 

 persthene and olivine from consideration it would doubtless 

 be possible to find types corresponding with those described by 

 Dr. Williams, but it would simplify matters in no respect. 

 The writer would express his obligations to Dr. Williams for 

 the kind loan of a series of typical sections from the main 

 Cortlandt with which to compare his results. As mineralogical 

 aggregates they are quite analogous. 



Around the edges of the area, where the massive rocks come 

 in contact with the gneiss, numerous small dikes have been 

 developed. They vary from one to several inches in width 

 and consist very uniformly of brown and green hornblende, 

 0*l mm to 0'3 mm intermingled with feldspar masses no larger. 

 The hornblende crystals tend to have their longer axes ar- 

 ranged parallel with the walls of the dike. The feldspar 

 rarely shows twinning and its composition must generally be 

 inferred from the analysis. The feldspar is however filled 

 with inclusions of hornblende, rutile, and less often apatite. 

 The following analysis (spec. 66a) kindly made by Mr. L. M. 

 Dennis, shows the notably high percentage of Ti0 2 , which 

 would be inferred from the slide. 



VI. 



Si0 2 49-93 



FeO* 2-74 



A1 2 3 . _ 24-64 



CaO 6-265 



MgO 2-426 



Ti0 2 6-007 



Na 2 2-204 



K 2 _■_ 3-797 



Loss on ignition 1 -2 



99-209 



The structure of most of these dikes is quite uniformly 

 allotriomorphic and in the majority of cases no amorphous 

 matter or distinct magma can be noted (exception mentioned 

 later). The hornblende has generally crystallized first after 

 the oxides but at least one instance (slide 68) has been re- 

 marked in which a plagioclase is included in hornblende. 

 Along the border of one small offshoot (66a) which is 4 mm 

 broad the microscope shows a selvage of fine quartz and feld- 



* All of the iron estimated as FeO. 



