130 Origin of Crystalline Limestone. 



recognisable. At Morel, in the commune of St Laurent 

 (Saone-et-Loire), crystals of pink orthose of an after develop- 

 ment exist in a limestone with Gryphcea arcuata, which 

 has a crystalline structure, but characterized by a grayish 

 yellow tint somewhat different from its usual colour. Lastly, 

 at Steinmal felspar crystals have been observed by M. von 

 Dechan in the inside of the abdominal buckler of a Homali- 

 notus. In the same manner, the transition graywackes in 

 the neighbourhood of Thann, and to the south of the Vosges, 

 are very often completely impregnated with felspar, and 

 still we find in them numerous remains of plants which have 

 been well preserved in spite of the later development of 

 crystals of felspar of the sixth system. 



The intimate and mutual penetration of the limestone and 

 gneiss, shews that both have been reduced to a plastic state, 

 if not to actual fluidity ; and the dissemination of the felspar 

 in the limestone mass, shews also that the gneiss must have 

 been sufficiently pasty for the felspar to have been secreted. 



The penetration of the limestone by the gneiss, as also 

 the undulations sometimes presented by both rocks at the 

 line of junction, make it evident that pressure was brought 

 into play to a great extent during the crystallization of the 

 gneiss ; this has produced in the limestone fissures generally 

 parallel to its line of contact with the gneiss, and compar- 

 able to those formed in a book the leaves of which are 

 squeezed or pressed back laterally. Those fissures have 

 been immediately filled by the secretions of matter diffused 

 in the limestone, and they have given place to the parallel 

 zones of nodular concretions, whilst the same matter formed 

 the veins or the lining in fissures of the gneiss. Although 

 in most of the metamorphic limestones the minerals are 

 especially developed in the natural joints, originating in 

 stratification, these nodules, on the contrary, in the limestone 

 of the gneiss of the Vosges, apparently owe their paral- 

 lelism to pressure. 



Pressure, like heat, has been also effective in actuating 

 molecular attraction, and in developing the different minerals 

 disseminated in the limestone. 



Subsequently to the crystallization of the limestone and 



