2 GEOLOGICAL MEMOIRS. 



The most extraordinary views respecting this rock, and particularly- 

 respecting the spots contained in it, were undoubtedly those of Buf- 

 fon. According to him, Porphyry consisted maiidy of the spines of 

 Echini, connected by a hard, strong cement pressed close together, 

 and which constituted the white points by which Porphyry was re- 

 cognized. Each of these white spots had a black point in the centre ; 

 this represented the nerve-cavity which extends through the whole 

 length of the spine of the Echinus. 



The fine porphyry of Esterel attracted the attention of naturalists 

 even in the latter half of the eighteenth century. The Swede Anger- 

 stein*, Buffonf, Saussure:];, Darluc§, and others allude to this rock. 

 Most of these descriptions, however, are obsolete and inapplicable to 

 the state of geological knowledge of the present day. The artists of 

 Rome employed the porphyry of Esterel in their works under the 

 name of Mordiglione. 



Older naturalists, who looked upon Porphyry as of neptunian ori- 

 gin, assumed that *'the enclosed portions of felspar" were older 

 than the porphyry itself; that they had been already hardened. 

 Pott — the chemist of Berlin, who died in 1799 — recognized the en- 

 closed particles or spots as ** sparry." The acicular hornblende, pe- 

 culiar to several kinds of porphyry, was regarded in older descriptions 

 of the rock as " Black Schorl." 



Towards the end of the eighteenth century, the word " Porphyry" 

 acquired another and more scientific meaning. Werner applied it to 

 the structure of the rock. He separated Porphyroid, as a general, 

 from Porphyry, as a special or particular term. Under the first he 

 classed those rocks, the matrix or paste of which contains single 

 grains or crystals, which have been formed contemporaneously with 

 the rock itself. The term "Porphyry" was restricted by him to 

 such porphyroidal rocks as belonged to a class, the paste of which 

 is homogeneous, and which especially contain imbedded crystals of 

 felspar. We are indebted to Gerhard for the first most important 

 and appropriate observation respecting this rock. 



After further details of the various descriptions and classifications 

 of diiferent kinds of Porphyry, our author continues, p. 4 : — 



L. von Buch is undoubtedly one of the first geologists who ob- 

 tained a clearer insight into the true nature of this rock. This is 

 particularly evident from his observations respecting the neighbour- 

 hood of Christiania : — "We must never forget that the compact 

 mass of all the porphyries is never a simple mineral : that its true 

 mineral ogical character, however, cannot be recognized, is due to the 

 circumstance of our vision not being capable of making out the mi- 

 nute individual particles." This was written in 1808. Godon also 

 expressed his doubt that all Petrosilex was one simple mineral. He 

 separated Petrosilex into "simple" and "porphyritic." 



Nevertheless the greatest uncertainty prevailed respecting Por- 



* Memoires des Savants Etrangers, vol. ii. p. 557, 1755. 

 t Histoire naturelle des Mineraux, vol. iii. p. 372. 

 t Voyages dans les Alpes, § 1436. 

 § Histoire naturelle de la Provence, vol. iii. p. 327. 



