Prof. T. G. Bonney — Ligurian and Tuscan Serpentines. 369 



aspect, and wavy outline of the surface of the strata, which dip at 

 some 15° away from the serpentine, are almost enough to prove the 

 latter intrusive. But by ascending the bed of a streamlet, and 

 climbing up a little to the right, more conclusive evidence may be 

 obtained. Here we have the section roughly sketched in the 

 annexed diagram. A talus, D, it is true, masks the actual junction 

 of the serpentine and the stratified rock ; but the state of the rock 

 in the little cliff is almost enough to prove intrusion. However, on 

 looking carefully about, I found a complete proof. At A, about four 

 yards from B, the last exposure of the serpentine, and six yards 

 from the base of the cliff (measured on the slope), and on a lower 

 level by a few feet, was a small slab of the stratified rock yet 

 adhering to the serpentine. This collocation places the intrusive 

 character of the latter beyond all doubt. 



Relations of Serpentine and Sedimentary Eocks, near Figline. 



C 



A Altered stratified rock. 

 C Stratified rock in situ. 



B Serpentine. 

 D Talus. 



Microscopic examination of a specimen from the upper part of 

 D has produced interesting results. It consists of a very fine muddy 

 or silty ground-mass, in most parts stained of a deep red, crowded 

 with minute organisms, some resembling Sponge spicules, often 

 triradiate ; others resembling Polycj'stinse or Foraminifera, such as 

 Orbulina or Lagena. They appear to be siliceous, and the internal 

 parts exhibit the black cross of aggregate polarization. Two or three 

 are pretty certainly minute Gasteropods. To determine the position 

 of the rest is not easy. One eminent student of Microzoa, to whom I 

 submitted the slide, claims the majority for Polyzoa, another for 

 Polycystinse and Sponge spicules. If I may presume, without 

 having made such organisms a special study, to express an opinion, 

 it would be that while some certainly much resemble Polyzoa, others 

 are singularly like Polycystinse. That all appear to be siliceous is 

 not conclusive, because under the circumstances replacement may 

 have taken place. Thus we are unable from these remains to fix 

 the precise geologic age of the rock, but still may fairly class it 

 with the strata of the immediate vicinity, which are, I believe, 

 Upper Cretaceous. 



DECADE II. — VOL. VI. — NO. VIII. 



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