2 Dr. H. H. Arnold=Bemrose—Olivine Nodules in Basalt. 
driven through the agglomerate on the northern slope of the hill into 
the basalt. It has, therefore, been possible for me not only to examine 
the relationship between the agglomerate and basalt, but also numerous 
blocks of the basalt, many of which contain olivine nodules. The 
largest nodule I have found is 2} inches in length, and from one trial 
hole I obtained forty-nine nodules in less than an hour. 
_In the level, which is about 50 feet in length, the agglomerate is at 
first in horizontal beds. Further into the hill the beds dip to the 
south. The dip increases until it becomes nearly vertical at the 
junction between the agglomerate and basalt. The agglomerate varies 
in coarseness and consists of basalt lapilli either in a limestone paste 
or in a volcanic detritus. The former kind is very similar to the 
agglomerate of Ember Lane, near Bonsall. The agglomerate of 
Calton Hill contains lumps of limestone, which are often more or less 
marmorized, pieces of basalt and inclusions of silica and calcite, which 
are several inches in length. ‘Two thin slices of these inclusions were 
examined. They consist of crystalline calcite and of quartz grains, in 
the form of a mosaic, and are probably a secondary aggregate of quartz 
and calcite. 
Tae Basatr or Catron Hin 
consists of olivine and big augite phenocrysts in a groundmass of small 
felspar laths, augite grains, and prisms, and magnetite or ilmenite. 
The felspars and augite prisms often show a well-marked flow- 
structure. The constituents of the rock are generally in a. fresh 
condition. The olivine, which is sometimes altered to serpentine 
along the cracks, occurs in phenocrysts and in groups of phenocrysts, 
and in irregularly shaped grains. ‘lhe augite appears as large pheno- 
crysts, often showing hour-glass structure, and sometimes containing 
portions of the groundmass, and in small prisms and grains. Both 
olivine and augite are found together in small nests or groups of crystals. 
The felspars sometimes occur in two generations and often exhibit 
a flow-structure. 
THe Nopvutes. 
The distribution of the nodules is general throughout the basalt of 
Calton Hill. In a hand-specimen they are easily distinguished and 
appear as a crystalline aggregate of bottle-green and yellow olivine 
with dark augite in the fine-grained and nearly black basalt. Some 
of the nodules are in a very fresh state; in others the cementing 
material between the grains has been dissolved away and the small 
grains may easily be separated by the finger. The nodules consist 
mainly of olivine, but contain a fair proportion of augite, and in some 
cases a small quantity of picotite. These minerals occur in irregularly 
shaped grains without any crystalline boundary, except in very few 
instances, especially near the outside of a nodule. The grains are not 
deformed crystals, but have hindered one another’s development as far 
as crystalline boundary is concerned. Fourteen thin slices from the 
nodules were examined. 
The olivine in the nodules is often traversed by cracks containing 
serpentine, and in some cases calcite and oxide of iron. Otherwise 
this mineral is in an unaltered condition. It sometimes contains 
