SPKINGS AND THOSE OBSERVED IN AMYGDALOIDS ETC. / 9 



1. In basaltic rocks — Auvergne, the Siebengebirge, theWetterau, 

 the Kaiserstuhl in the Grand Duchy of Baden, the Mittelgebirge in 

 Bohemia, the Euganean Hills and the neighbourhood of Rome, the 

 Cyclopean Islands near Sicily, the Tertiary volcanic region of Antrim, 

 and the west coast and islands of Scotland, Faroe, Iceland, parts of 

 Greenland, and certain districts in India and Australia. 



2. In the more ancient eruptive rocks, melaphyre and diabase — 

 the Southern Tyrol, especially the Fassa-Thal, the neighbourhood of 

 Oberstein and Idar in the Pfalz, Giromagny in the southern part of 

 the Vosges, Nassau (in Schaalstein), the Harz (in Blatterstein), 

 Thiiringen, the Isere (in the variolite or spiliteof Drac), Lake Superior, 

 Nova Scotia, Connecticut, Central Africa, &c. 



That these minerals are not to be considered mere adventitious 

 accretions to the rocks containing them, is evident from the large pro- 

 portion that the zeolitic kernels often assume in relation to the whole 

 mass. Thus, according to Boue*, in the Isle of Skye stilbite is found 

 at times in nests from 4 to 5 feet in diameter, and makes up a nota- 

 ble portion of the rock. The same thing is seen in the Cyclopean 

 Islands, where analcime is found abundantly, both in nodules and 

 in veins ; as well as in Faroe, Iceland f , and other places. In addition 

 to these voluminous masses, the same minerals are often sufficiently 

 abundant in certain parts of the rocks to form an important propor- 

 tion of their total bulk. Thus in the Wetterau, according to the 

 observations of Tasche ;£, chabasite and christianite are present in the 

 compact portions, in addition to filling the cavities, of the basalts ; 

 and these minerals can generally be recognized in thin slices of these 

 rocks, when examined by the microscope, as, for example, in the 

 basalt of Donnersberg and other localities in Bohemia. 



The minerals associated with zeolites may also form important 

 elements in the constitution of the class of rocks under discussion. 

 In evidence of this we have the fact, recorded by Boussingault, that 

 the crystalline rocks of the Andes, with very few exceptions, contain 

 carbonates, as shown by their effervescence when treated with acid. 

 The spilites of Drac || in the same way lose 10 per cent, by weight 

 when finely powdered and heated with a weak acid, lime with a 

 little magnesia and iron being found in the solution. At Obercastel, 

 near Bonn, siderite is found in basalt, not only filling geodes but 

 forming part of the paste or substance of the rock, where it is as- 

 sociated with a considerable proportion of zeolites ; and similar con- 

 ditions of association are recorded in the basalts of other parts of the 

 Siebengebirge and of the Wetterau §. 



The minerals chlorite and green earth, which have been proved 

 both by microscopic and chemical investigation to form component 

 parts of many of the so-called basic rocks, appear also to be the result of 

 decomposition, as some of the mineral constituents of the latter, more 



* ficosse, pp. 238-245. t Sartorius Ton Waltershausen. 



+ Schotten, pp. 52-57. 



|| Gaymard, Ann. des Mines, 4 e ser. vol. xviii. ; Lory, 'Isere,' p. 136, 

 § Von Dechen, ' Siebengebirge,' 2nd ed. p. 149. Mitteldeutsche geol. Karte, 

 descriptions : Schotten, pp. 52-57; Alsfeld, p. 51 ; Lauterbacb, p. 64. 



