52 Recent Excavations at Stonehenge. 
All of these various features may be found in different specimens 
of the sarsens which occur among the fragments found in the 
excavations at Stonehenge. Of the relative paucity of the fragments 
of sarsen found in the excavations, when compared with those of 
the “bluestones” and other rocks, I shall have to speak further in 
the sequel. 
Il. Ophitic Diabase.—These rocks have been fully described by 
Professor Maskelyne, and all the varieties which he mentions as 
occurring in the “bluestone” monoliths of Stonehenge find their 
parallels among the fragments collected in the recent excavations. 
the rocks differ greatly in size of grain, some being coarse-grained 
and porphyritic, others being comparatively fine-grained and almost 
compact in structure. The ophitic character is in some cases much 
more marked than in others. The rocks differ also greatly in the 
amount of alteration they have undergone. In some cases the 
felspar (labradorite 7), the augite, and the magnetite or titanoferrite 
are all quite fresh and unchanged, so that the rock might be called 
an “ophitic dolerite.” More frequently the felspar has been 
largely converted into epidote and zoisite (with secondary albite), 
the augite into various chloritic minerals, and the titanoferrite 
into leucoxene. 
Ill. Highly altered Basie Tuffs and Agglomerates.—These rocks 
are generally of a fissile character, and some of them have been 
variously referred to by different authors as “schistose rocks” and 
“calcareous chloritic schists.” They consist of chlorite and 
leucoxene, with various colourless minerals (zoisite, albite, etc.), 
the products of the alteration of minerals found in basic lavas. In 
many cases the rock is evidently made up of more or less angular 
fragments, and not unfrequently these fragments are vesicular, the 
vesicles being filled with crystalline calcite. In consequence of 
this, most of these rocks effervesce freely with acid. It is evident 
that the rocks are of volcanic origin, and are ancient basic tuffs 
and agglomerates. In some cases the amount of alteration which 
they have undergone is extreme ; only traces of their original clastic 
character can be detected, and the rocks have evidently become 
‘more or less foliated in structure. The number of fragments of 

