﻿Geology and Mineralogy. 239 



there is no reason to doubt, in the present state of petrological 

 and metamorphic science, that if detrital augite or hornblende or 

 biotite were present in the sediment, more or less biotite, or 

 chlorite, or garnets, or hornblende might be formed. 



Hence with even the metamorphic change producing a hydro- 

 mica schist, the disappearance of fossils is to be expected, though 

 not always a fact ; and that producing a coarse mica schist neces- 

 sarily exterminates fossils. In conclusion, I believe we may safely 

 regard the Canaan fossils as proof that the limestones and schists 

 of the Taconic system are not older than the Potsdam sandstone. 

 In June last, Professor D wight discovered another locality of 

 fossils at Canaan, and the locality has afforded Ophileta and 

 Holopea-Wke forms, besides others, with numerous small crinoidal 

 disks ; and some of the Ophileta-like shells are nearly two inches 

 in diameter. He is at work studying the species and will soon 

 report upon them. 



6. Tertiary Ophiolitic and basic rocks of Scotland and Ire- 

 land. — Signor B. Lotti (Boll. Com. Geol., April, 1886, p. 73) 

 reviews two recent papers of Prof. J. W. Judd : the Tertiary and 

 older peridotites of Scotland (Q. J. G. Soc, xli, 354, 1885), and 

 the Gabbros, dolerites and basalts of Tertiary age in Scotland 

 and Ireland (ib., xlii, 49, 1866), and presents somewhat similar 

 facts from the Tertiary formations of Italy. Mr. Judd shows 

 that the igneous rocks of the Western Isles of Scotland, of Faroe 

 Island and northern Ireland, which are similar and of Tertiary 

 age, include gabbros (olivine-gabbros of some authors), dolerytes, 

 basalt and basalt-glass ; that there is a gradual passage from 

 coarse gabbro, of true granitic type of texture, to tachylyte or 

 basalt-glass ; that porphyritic kinds occur in the several terms of 

 the series down to that of basalt-glass; that unaltered and altered 

 kinds of several of the rocks occur, and that neither differs from 

 similar rocks of pre-Tertiary age ; that the altered forms include 

 saussurite-gabbro (having the feldspar changed to saussurite and 

 the augite more or less to foliated hornblende) ; that the gabbro 

 passes into picryte by the disappearance of the feldspar, into tro- 

 cholyte by the disappearance of the augite, and into eucryte by 

 the disappearance of olivine ; that the gabbros, dolerytes, basalts 

 and tachylytes do not present any essential difference in their 

 bulk-analyses ; that, in the incipient stage of change, augite often 

 assumes the foliated structure of diallage and lustre of bronzite 

 or schiller spar, a process which Mr. Judd names schillerization, 

 and that it may pass thence, by further change, into serpentine, 

 though the alteration of olivine is the common source of the ser- 

 pentine. 



Signor Lotti cites also the paper of Hague and Iddings with 

 regard to the gradation between granitoid and basaltic forms of 

 the same igneous mass in Nevada. He describes the ophiolitic 

 Tertiary rocks of Italy as intersecting and interlaminated with 

 Eocene strata; as including euphotide (gabbro), diabase (doler- 

 yte), and serpentine ; the euphotide as labradoritic, or saussuritic 

 (most common), or olivinic, or serpentinous (very common), and 



