48 Recent Excavations at Stonehenge. 
been derived.t He refers other rocks to the “compact felspar of 
Macculloch.” 
The same author in 1871 recorded the finding of shells in one 
of the blocks of sarsen at Stonehenge.” 
In 1877 there appeared the very valuable essay of Professor N. 
S. Maskelyne on the “ Petrology of Stonehenge.* As the result of 
a careful study of very minute chips taken from the monoliths of 
Stonehenge Professor Maskelyne, who was assisted in the research 
by the late Mr. Thomas Davies, of the British Museum, classified 
the stones as follows: i. Sarsens. ii. The “grey micaceous grit of 
the ‘altar-stone.’” iii. Different varieties of “diabase” (including 
the majority of the so-called “ bluestones”) in which it was shown 
for the first time that augite and not hornblende was the predomi- 
nant mineral. iv. Hornstones, of which it was found that four 
stones consisted, two of them having a “schistose structure.” The 
microscopical characters of these rocks were illustrated in a plate, 
and analyses of the types iil. (Stone 33) and iv. (Stone 48) made 
by Dr. Prevost are given. 
Professor Maskelyne in this paper refers to the numerous frag- 
ments and chips of rock found in the soil of Stonehenge, and points 
out that they are generally identical with the stones of the structure. 
He classifies them as: i. Diabasic dolerite and felsitic rock, some 
possessing the distinctive features of the “ bluestone” monoliths of 
Stonehenge (these are very abundant). ii. Compact rocks with 
slaty cleavage. ili. Quartzoze grits, with scales of brown mica or 
green grains (chlorite ?). Professor Maskelyne’s essay called at- 
tention to the great importance of the study of the monoliths of 
Stonehenge, and of the fragments buried in the ground within and 
‘See letter from Professor Phillips to Dr. Thurnam quoted in Long’s 
“Stonehenge and its Barrows,” Wilts Archeological and Natural History 
Magazine, xvi. (1876), 71. 
* John Phillips, Geology of Oxford and the Valley of the Thames (1871), 447. 
% Wiltshire Archeological and Natural History Magazine, xvii. (1877), 
147-160, with plate. See also Proceedings of the Geological Association, 
-vii., 138-140. 

