A. Wandke— Study of Cape Xeddick Gabbro. 303 



fifty, fifty and one foot from the contact; the other of 

 three specimens taken fixe, three and one foot from the 

 contact. In each of the thin sections made from these 

 specimens recrystallization of the original minerals and 

 the addition of material are indicated by the development 

 of feldspar, diopside, biptite, epidote, brown hornblende, 

 calcite, magnetite, and pyrrhotite. In the specimens 

 taken one-hnndred-fifty feet from the contact the diopside 

 and other minerals as listed above are not abundantly 

 developed. But as the contact is approached both feld- 

 spar and diopside increase greatly in amount. The feld- 

 spar which at a distance consisted of orthoclase and albite 

 is decidedly more basic and of larger grain near the 

 contact. 



The amount and kind of alteration of the quartzite also 

 shows slight variations. Thus a specimen taken five feet 

 from the southeast contact is characterized by an abun- 

 dance of andesine feldspar which is replacing the quart- 

 zite. The development of the plagioclase was evidently 

 so rapid that portions of the original quartzite were 

 incorporated within the plagioclase, the result being 

 grains of feldspar loaded down with inclusions. At the 

 contact diopside is a dominant mineral and quartz, 

 although present, occurs in decidedly less abundance than 

 one-hundr eel-fifty feet from the contact. A specimen of 

 quartzite from within the hybrid contact zone of the 

 gabbro was also sectioned. The section shows a remark- 

 able development of diopside which suggests that this 

 mineral was soaked up by the quartzite as a sponge 

 soaks up water. The presence, moreover, of hornblende, 

 biotite, apatite, magnetite and pyrrhotite would indicate 

 that the rock which started as a slightly argillaceous 

 quartzite now has the composition of a quartz cliorite. 

 Thus there is a tendency for the contact phase of the 

 sediments by the addition of material from the gabbro to 

 approach a gabbro as far as mineral composition is con- 

 cerned and to resemble the phase of the gabbro which 

 has been altered by the assimilation of quartzite. 



