EELATION TO MESOZOIC EOCKS IN THE LEPONTINE ALPS. 235 



preserved, but in proportion as the fine granular look of the cal- 

 careous organism is lost and a regular mineral cleavage set up, these 

 structures tend markedly to disappear *, The slide contains one of 

 the rounded mineral spots, but these and the prisms are not 

 abundant in the hand-specimens. 



Near the base (apparently) of the similar group of rocks on the 

 Alp Vitgira is a curious-looking nodular rock, which, in the field, 

 appeared to me as if it were mainly composed of fragments, were, in 

 short, a conglomerate or breccia at the base of the Jurassic series, 

 much crushed. It exhibits, under the microscope, a very peculiar 

 structure. The chief constituents are calcite, quartz, white mica, 

 brown mica, sometimes altered into a greenish mineral, and garnet. 

 This is speckled with " opacite," which also is variably dissemi- 

 nated in the slide. A bit of the slide here and there resembles the 

 ordinary matrix of these Jurassic rocks, and one small fragment 

 resembles an organism (Pentacrinites2). The structure of crushed 

 breccias in the Alpine Palaeozoic and Mesozoic rocks is often peculiar, 

 the ultimate result of the pressure being to render the fragmental 

 structure less definite, probably by the direct effects on the frag- 

 ments themselves and the "mashing up" of chips from their 

 surfaces with the very variable constituents of the matrix. Thus 

 it becomes difficult to discern the precise boundaries of the fragments 

 and of the matrix, or to be sure in many cases whether we have 

 (more especially in the case of quartz and calcite) minerals of 

 primary or derivative origin. But in regard to this slide, I may 

 say that the garnet, at any rate, appears to be distinctly derivative. 

 It occurs in two ways. One piece resembles a garnet which has 

 been partly broken up and recrystallized. There is a piece, like the 

 remnant of a crystal, about '1 inch long and one third of this wide, 

 which passes on both sides into a granular mass of garnet, quartz, 

 and a little brown mica. The others exhil)it a mass composed of 

 garnet, calcite, and quartz, with a very little brown mica, the first 

 mineral appearing to act as a kind of setting to the others, the 

 interspaces composed of it being elongated in one direction, so that 

 the garnet seems to form a kind of root-like growth among the 

 other minerals. This structure I consider to be a record of pres- 

 sure ; it is a species of foliation ; but I observe that, while usually 

 it is parallel with the structure of the rock-mass which is due to the 

 Post-Jurassic movements, at least in two specimens, which have a 

 very frkgmental aspect, it lies athwart the latter. This " foliation " 

 accordingly appears to be of earlier date than the Jurassic epoch. 



* I have observecl the same thing in regard to the so-called canal-system in 

 the supposed oi-ganism Eozoon canadensc. [In the discussion it was stated that 

 " marmorosis " had taken place in the organisms in these Jurassic rocks. In 

 those described here there is just as much or just as little "marmorosis" as 

 may be seen in any later Pahuozoie limestone in Great Britain. The Belem- 

 nites, being larger and rather brittle, are a little more changed in apj^earance, 

 but even these riot seldom, on careful examination with a lens, are found to 

 retain tl\eir characteristic structure. If these slides exhibit " marmorosis," so 

 do hundreds of limestones to which no one would apply the term " meta- 

 raorphic," using this in its ordinary sense.] 



