472 J. H. COLLINS ON THE SERPENTINE AND 
districts did not differ so much as Mr. Collins supposed. As a mica- 
ceous series in each case appeared below hornblende-schist, the 
speaker had supposed them identical. How the granite, which Mr. 
Collins supposed was intrusive in Lower Silurian, was to appear in 
a Lower Silurian conglomerate, he failed to see; also, why the ab- 
sence of an overlying series need be explained; or why, if a bed 
showed just by a fault, it was therefore reduced in thickness. Mr. 
Collins’s argument as to the non-identity of these micaceous schists 
at Polpeor and Porthoustock was misleading. He had selected a 
very exceptional rock from the one place, and compared it with one 
of a more normal type from the other. On such a method of arguing 
he would not comment in the author’s absence. 
Mr. Hupieston thought that Mr. Collins advocated something 
like the “ transmutation” of the old alchemists. He asked how the 
alumina could be got rid of ; it was most difficult to explain such 
aseparation. The suggestion sometimes made that serpentine might 
have been formed by the alteration of gabbro, though highly im- 
probable, was more likely than the idea of the change of hornblende 
schist into serpentine. 
Prof. Szetey regretted the absence of the author, and cited 
certain cases of reputed changes of the same kind queted by 
Giimbel in the Fichtelgebirge, by Zirkel in the Schwarzwald, and 
by other authors. 
Mr. Txatt stated that one of the best-authenticated cases of the 
formation of a substance having the composition of serpentine by 
the alteration of hornblende had been investigated by Weigand. It 
occurred in the Vosges. The serpentine, however, was associated 
with chlorite, in which the alumina, originally present in the horn- 
blende, was doubtless contained. The microscopic structure of this 
serpentine was moreover very different from that of serpentine 
derived from peridotite. Other asserted cases of the formation 
of serpentine by the alteration of hornblende rocks had been 
recently investigated by Schultze, and always with the result 
that the true serpentines gave evidence under the microscope 
of having been originally olivine rocks. There were two ques- 
tions involved :—one was the nature of the rock which by its 
alteration gave rise to serpentine, and the other was the rela- 
tion which this rock bore to the associated hornblende-schists and 
gabbro. On the first point all recent observers were agreed that a 
serpentine showing under the microscope the net-like structure 
(Maschenstructur of the Germans) described by Prof. Bonney as 
characteristic of the Lizard serpentines had been produced by the 
alteration of olivine rocks. On the second poimt, however, there 
was by no means unanimity of opinion; and cases described by 
Kalkowsky in the Eulengebirge, in which olivine occurred as an 
accessory in the hornblende rocks and hornblende in the serpen- 
tines, appeared to show that sometimes the two rocks were very 
intimately connected. 
Rev. E. Hitz said that one of the serpentines of Porthalla is 
remarkably laminated; but he thought the lamination was due to 
