INDICATIONS OF FLOWAGE IN THE BASIO ROCKS. 139 
angular particles, but all turned out to be completely crystalline rocks, 
owing their appearance of a fragmental nature to decomposition. 
The more massive beds of basic rocks, or the lower massive portions 
of such beds as possess the crowning amygdaloids, are often without any 
definite structure. This is the common case in the typical region of 
Keweenaw Point, where a few beds only show a tendency to a transverse 
columnar structure. On the Montreal River, however, this structure is 
well developed in a series of quite thin’ beds, which are furnished with very 
perfect amygdaloids, and stand about vertically. On the Minnesota shore, 
a columnar structure is the rule, and since the beds lie at a very flat angle, 
cliffs of vertically columnar rocks are a prominent feature. Still, the struc- 
ture never reaches a great perfection. 
Allusion has been made above to the elongated vesicles of some of the 
amygdaloids. Other indications of flowage sometimes to be seen in con- 
nection with the more massive rocks are a slaggy or ropy texture, and an 
appearance as if a once solidified crust had broken, and the several frag- 
ments reunited by further solidification, suggesting the “‘clinkers” of mod- 
ern volcanic regions. These appearances, while noted at a number of 
points, are not common. They are merely additional indications of the 
once fluid condition in which all of these basic rocks are sufficiently proved 
to have been by the common division into amygdaloidal (vesicular) and 
compact portions; by the mineralogical composition—augite, plagioclase, 
olivine, magnetite; by the completely crystalline condition; by the flowage 
lines formed by the tabular plagioclases in some of the finer-grained kinds, 
and by the occurrence in some of the kinds of remnants of the original 
glass magma. ‘The interstratification of these rocks with wholly unaltered 
sandstones and shales must preclude at once any thought of a metamorphic 
origin. As already indicated, I can only regard these beds as true lava 
flows, owing their interstratification with the accompanying sediments to 
their having been poured out at surface while the sediments were forming. 
A very beautiful additional proof of contemporaneousness is furnished 
by the peculiar relation of a sandstone to its immediately underlying crys- 
talline rock, the sand penetrating the openings and cracks in the latter. A 
number of places were noted on the North Shore where the overlying sand- 
