776 THE GEOLOGY OF MINNESOTA. 



[Gabbro. 



No. 1747. GABBRO. (Mitch altered.} 



North side of the headland, twenty-five feet above the water. 

 Ref. Annual Report, xxi, page 157. 



Meg. A much-decayed, coarse diabase or gabbro. 



Mic. Quartz, dial I aye, Icmurcni' and a much-changed feldspar, are the only 

 identifiable minerals. One (thick) section. 



Age. Cabotian(?) N. n. w. 



No. 1748. GABBRO. (Mm-h nU<-nd.) 



North side of the headland, at fifty feet above the lake. 

 Ref. Annual Report, xxi, page 157. 



Meg. Similar to the last. 



Mic. Diallage, uraUte, leucoxene, quartz and an indeterminable, much-altered 

 feldspar, with zolsite, etc. One (thick) section. 



Aijc. Oabotian(?) N. H. w. 



No. 1749. GABBRO. (Much a/fi-ml. ) 



North side of the headland, at the northern crest of the hill. 

 Ref. Annual Report, xxi, page 157. 



M<>g. Resembling gabbro. 



Mic. As in the foregoing from this rock, the feldspar is entirely destroyed, as 

 well as the olivine. There remain leucoxene, and a form of pyroxene (apparently in 

 some cases diallage), as the only relics of the original minerals. Quartz has entered, 

 most of the pyroxene is converted to uralite, and the spaces of the original feldspars 

 are filled with a variety of decomposition products, which unfortunately, on account 

 of the great thickness of the slides made from this rock, cannot be differentiated, 

 but in which zoisite plays a leading part. One section. N. H. w. 



Age. Cabotian(?) 



No. 1750. GABBRO. (Much altered.) 



Top of the headland, perhaps 250 feet above the lake, near the centre of the promontory. 

 Ref. Annual Report, xxi, page 157. 



Meg. Gabbro-like. 



Mic. Iii this slide the structure is sufficiently preserved to show that it was 

 ophitic. The leucoxene shows a coarse sagenite structure of rutile, but is still only 

 sub-translucent. One (thick) section. 



Age. Cabotian(?) N. H. w. 



No. 1751. GABBRO. (Hfuch altered. ) 



Near the southern crest of the headland. 

 Ref. Annual Report, xxi, page 157. 



Meg. Similar to the last. 



