170 General Notes. 
original plagioclase from which the scapolite was derived. Inclu- 
sions of dust and fluid cavities are present in the scapolite in large 
quantities and microlites are developed along its cleavage planes. The 
rutile occurs in grains closely associated with the scapolite. In 
several instances these grains appear to be made up of lamellae, in 
which, however, there is no alternation of extinction as in the case 
of polysynthetic twins. The authors call the rock a scapolite-dio- 
rite. A rock from McDougall, Parry Sound District, contains a 
basic pagioclase in addition to the minerals mentioned above, and 
has been called plagioclase-scapolite-diorite. Schistose rocks with 
the composition of the last mentioned diorite, have had their schist- 
isty produced in them by pressure, as is evident from the shattered 
condition of the plagioclase constituent. The scapolite in these 
rocks bear no marks of a secondary origin from plagioclase. Augite 
is lacking, but biotite and quartz are observed in addition to the 
minerals found in the diorites. — The dolerites ^ of Londorf, Hes- 
sec, embrace coarse and fine grained varieties as well as glassy 
phases. The former consists of plagioclase, a titaniferous augite, 
olivine, a little enstatite, magnetites, apatite and titanic iron. The 
olivine is a pure hyalosiderite, elongated in the direction of the c 
axis, and inteigrown with plates of titanic iron in such a way that 
these are perpendicular both to the cleavage planes and to the long 
axes of the olivine crystals. Amygadaloidal cavities contain the rock 
forming minerals together with little crystals of hornblende, and 
tridymite and masses of hyalite. To account for the existence here 
of well developed crystals of the minerals occurring in the body of 
the rock, Streng supposes the bubble of gas which gave rise to the 
cavity to have moved along through the partly solidified magma, 
shoving out of its way the liquid portions and leaving the crystals 
free. Other substances are supposed to be due to the alteration of 
the glass which was left attached to the crystals. The hornblende 
is regarded as having been deposited from the hot solutions, which 
would naturally circulate through the amygdaloidal cavities. The 
sublimation theory proposed to explain the existence of druse min- 
erals in cavities of eruptive rocks he dismisses as unsubstantiated by 
facts. Upon the surface of the glassy dolerite is a crust of altered 
material with the characters of palagonite. — Lcewinson-Lessing * 
• has embraced in a very readable article the views which are gradually 
becoming prevalent among petrographers in reference to the origin of 
diabases, gabbros and diorites. After briefly calling attention to the 
acknowledged differences between the structure of intrusive and effu- 
sive rocks, and emphasizing the peculiar features of the diabase struct- 
ure, the author declares that this is the structure of an effusive rock 
rather than of an intrusive one. The association of diabases with 
fossil-bearing tuffs and their gradation into augite-porphyrites leads 
him to regard them as effusive under water, with the augite-porphy- 
. 1888. II. p. 181. 
