182 
PROCEEDINGS 1841 — 1848. 
between the wholly re-constituted granite and original stratified mass 
some incompletely altered rocks of the kind usually termed meta- 
morphic. He brought forward some experimental results in confirma- 
tion of his opinion, which he also supported by a considerable 
experience in the volcanic regions of Europe. Mr. Marshall's papers 
on this subject will be found in the reports of meetings of the British 
Association for the years 1839, 1858, and 18G1. The explanation 
offered by ]\lr. Marshall of these plienomeua proceeds on the supposi- 
tion that the strata of the district had been exposed to the action of 
the general heat of the globe by reason of the depression to which 
they had been subject, that this general heat has been productive of 
effects varying with the nature of the rock, and graduated by the 
scale of applied heat, granite being the extreme term of metamorphism, 
viz., complete fusion followed by re-crystallisation, the whole meta- 
morphic tract being subsequently subject to displacement. Professor 
Phillips, in his presidential address to the Geological Society in the 
year 1859, whilst referring in eulogistic terms to the researches of 
Mr. Marshall, says : — " The general conclusion to which Mr. Marshall 
has been conducted in the course of his long study and intimate 
knowledge of the Lake Mountains is thus expressed. The phenomena 
observed may be best explained by the supposition that the w^hole 
series of rocks (granites included) are metamorphic sedimentary 
strata {?i situ, or in their original order of position, and that the 
slatey rocks alternating with the porphyries are to be accounted for 
on the supposition that they are by chemical composition less 
fusible, less easily acted upon by heat than the porphyritic beds, 
and have therefore been only hardened, retaining the cleavage 
and stratified structure, whilst the more fusible rocks have been 
changed into porphyries. This supposed original inequality in 
the degree of fusibility has been in some degree submitted to the 
test of experiment. Portions of the Skiddaw slate, green slate, and 
porphyritic bands in powder have been placed in crucibles and gradually 
heated ; at a good red heat the porphyry puffed up, fused and ran 
over the edge of the crucible in the shape of a brown glassy slag ; 
at a white heat the Skiddaw slate fused into a grey glassy slag ; and 
lastly, at a strong white heat the green roofing slate also fused into 
