BASALT-GLASS OE THE WESTEEX ISLES OF SCOTLAND. 445 



" pitchstone ;" and the fact is recorded by the latter author in the 

 Transactions of the Geological Society*. 



In 1829 Boue f referred to the two cases of basalt passing into 

 glass already described by Macculloch ; and it was probably on 

 specimens carried to Paris by Boue that Delesse made the interest- 

 ing observations to which we shall refer in the sequel. 



On the Continent, the first clear recognition of the distinction 

 between the basic and acid glasses appears to be due to Breithaupt 

 in 1826. Klaproth|, it is true, had as long ago as 1807 described 

 a "black fossil " from Guilian a in Sicily as " slaggy augite ;" and 

 this substance is now generally regarded as belonging to the class 

 of basalt-glass ; but to Breithaupt § we owe the precise indication 

 of those characters by which the basic glasses are distinguished from 

 similar materials of different composition. Breithaupt regarded the 

 substance which he obtained from the Sasebiihl between Gottingen 

 and Dransfeld as a new mineral species, and indicated its distinctive 

 properties with great precision. He proposed for it the name of 

 " tachylyte," signifying the rapidity ivith luliich it undergoes fusion || 

 before the blowpipe. It is worthy of remark that the author of the 

 species and his followers on the Continent down to quite recent 

 times regarded the substances of this class as minerals and not as 

 rocks. 



In 1840 Gmelin % described a somewhat similar substance from 

 the Yogelsgebirge (probably from Bobenhausen) ; and in 1841 

 Elipstein ** gave more precise information concerning the mode of 

 occurrence of this material. In 1844 Hausmann ft gave a new 

 description of the substance from the Sasebiihl, accompanied by an 

 analysis by Schnedermann ; and he connects with it a tachylyte- 

 like " fossil " from the Wetterau, which GmelinJJ, four years before, 

 had analyzed and referred to augite. In 1847 Hausmann §§ sepa- 

 rated the Bobenhausen material from tachylyte as another mineral 

 species under the name of " hyalomelane," though the grounds of 

 this division do not very clearly appear. 



* Trans. Geol. Soc. vol. ii. p. 359. The veins of Carsaig in Mull, with which 

 the Beal dyke is erroneously compared, are formed of a black pitchstone which is 

 of acid composition, containing 68 per cent, of silica. A similar comparison 

 is made by Lyell and Murchison, Edin. Phil. Journ., July 1829. 



t Essai geologique sur l'Ecosse, p. 284. 



| Eeitrage zur chemischen Kenntniss der Mineralkorper, vol. iv. p. 190. 



§ Kastner's Archiv fur die gesammte Naturlehre, vol. vii. p. 112 (1826). 



|| A great amount of confusion has taken place with respect to this name 

 "tachylyte." It has been frequently written " tachylite," " tachylith," and 

 even " trachalite." Naumann and others state that the rock is so called from 

 the ease with which it is decomposed by acids. A reference to Breithaupt's 

 original memoir shows that the spelling and origin of the name are as stated 

 in the text. The name " bottleite," said by Kinahan to have been locally given 

 to it, does not appear to have come into any general use. 



% Poggendorff s Annalen, vol. xlix. p. 233. 



** Neues Jahrbuch fur Min. &c. 1841, p. 696. 



tt Studien d. gottingischen Vereins bergmann. Freunde, vol. v. p. 91. 



\\ Neues Jahrbuch fur Min. &c. 1840, p. 549. 



§§ Handbuch der Mineralogie, zweiter Theil, vol. i. p. 545. 



