INTRODUCTION. 99 



Spallanzani's experimental researches were published in 

 several volumes in the same series as the more popular descrip- 

 tive account of his travels (Travels in Sicily and some parts 

 of the Apennines, 6 vols., Pavia, 1792-97). His descriptions 

 and observations of volcanic regions surpass in scientific 

 accuracy and completeness all previous contributions of the 

 kind, and have secured a permanent place in the literature 

 of scientific travel. Although Spallanzani's numerous experi- 

 ments invariably produced vitreous rock-varieties, Hall suc- 

 ceeded shortly after in demonstrating that crystalline structure 

 could be produced experimentally by the slow cooling of melted 

 rock. 



In 1801, Scipio Breislak (p. 78) published a descriptive and 

 geological work on the Phlegrsean fields, the extinct volcanoes 

 near Rocca Monfino, on Monte Somma, Vesuvius, the Baise, 

 Procida, and Ischia. This work comprises several maps, and 

 is in many respects supplementary to Spallanzani's Travels. 

 Breislak also contributed the first researches on the geology 

 and stratigraphy of Rome, and of that part of the Apennines 

 which surrounds the volcanic area of the Italian mainland. 



Leopold von Buch was also a contributor to the geology 

 of Rome. His study of the basalt of Capo di Bove and the 

 Alban mountains aroused in his mind the first doubts of the 

 correctness of Werner's Neptunian doctrine. The best feature 

 in Von Buch's summary of the geology of Rome is his lucid 

 exposition of the travertine and tuff deposits. He demonstrates 

 that these are true aqueous sediments, although he recognises 

 the volcanic origin of many of the contained mineral fragments. 



In a paper "On the Formation of Leucite," Von Buch tried 

 to prove that the crystals of leucite in the lava had separated 

 out while the material was still in a fluid state. In his estima- 

 tion the leucite crystals were original volcanic products; he 

 discredited the hypothesis that they had been originally 

 components of an aqueous sediment which had been 

 partially melted in subterranean volcanic cisterns and poured 

 forth as lavas. The anti-Neptunian attitude assumed by 

 Von Buch in this paper was turned to good account at the 

 time by the Volcanists. But Von Buch still held a somewhat 

 contradictory position regarding basalt. 



After he had visited Vesuvius and the Euganean Isles, in 

 1799, he wrote to Pictet that little -difference could be 

 distinguished between the lava flow from Torre del Greco 



