America?i Association Meeti/ig. 263 
of the greenstones vary to more silicious rocks, constituting great 
thicknesses of graywackes, phyUites and conglomerates, and as such 
have been converted by widespread metamorphism into mica schists 
and gneisses, the akeration coming on by degrees, increasing in 
intensity toward centers of granitic intrusion, and toward the great 
areas of granite and igneous gneiss. 
Such granite and such metamorphic rocks, as a whole, have been 
considered the basement rock, the oldest known rocks of the country. 
But, following up the long known fact that the Laurentian granite 
ard igneous gneisses cut the schists and sedimentary gneisses and 
hence are younger, they are in the same way shown to be younger 
than the bottom greenstones. They occasionally penetrate these 
greenstones and change them to amphibolyte and pyroxene gneiss. 
These metamorphic schists and gneisses seem to be a representative 
of the sedimentary portion of the Lower Laurentian of Canada, while 
the igneous granite and gneisses are as plainly a general parallel of 
the igneous portion of that series. It follows therefore that the Cana- 
dian Laurentian is, as a whole, of later date than the greenstones, 
if the succession is the same as in the Northwest, and that the 
greenstones should be considered the bottom rock of the geological 
scale. 
21. The Origin of the Archean Igneous Rocks. By N. H. 
WiNCHELL. To be published in the American Geologist. 
22. Joints in Rocks. By Prof. C. R. Van Hise, Madison, 
Wis. (Read by title). 
22,. Notes on Some European Museums. By Dr. E. O. Hovey, 
American Museum of Natural History, New York City. Relating 
to administration and display of specimens; to be published in the 
American Naturalist. 
24. History of the Blue Hills Complex. By Prof W. O. 
Crosby, Boston, Mass. The complex of the Blue hills, on the 
southern border of the Boston basin, is a small part of the great 
granitic bathol ite of eastern Massachusetts, inclosing isolated masses 
and belts of Lower and Middle Cambrian strata. The Cambrian beds 
are cut by a series of diabase dikes older than the granites. The 
granitic series, which clearly constitutes one genetically related or 
consanguineous group, comprises: 
I. Plutonic rocks: i. Normal granites, forming the main body 
of the bathol ite: (a) biotitic normal granite (granitite) ; (b) horn- 
blendic normal granite. 2. Rocks forming the contact zone of the 
bathol ite: (a) dioryte and basic granite (granodioryte) ; (b) fine gran- 
ite: (c) quartz porphyry, passing into a basic, quartzless porphyry. 
II. Intrusive or dike rocks not occurring as apophyses of the 
contact zone :(a) microgranite; (b) aporhyolyte. 
III. Effusive or volcanic rocks: (a) aporhyolyte (compact and 
duidal forms). 
