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HARDWICKE'S SCIENCE- GO SSIP. 



GEOLOGY. 



Carboniferous Laud-shells. — Dr. Dawson 

 has described the occurrence of a large number of 

 a carboniferous land-shell {Pupa vetusta) in South 

 Loggias, Nova Scotia, inside an erect Sigillaria 

 trunk, above two thousand feet above the stratum 

 where this shell was first met with. Two other 

 carboniferous laud-shells, Pupa vermilionensis and 

 Bawsonella MeeJci, have also been found in the coal- 

 field of Illinois. 



"Missing Links."— Professor Marsh is now 

 arranging the vast collection of animal remains 

 found in the West, and announces two additional 

 fossil birds possessing teeth implanted in sockets. 

 One is a new species of the first division, Hesperor- 

 nis, and the other forms the type of a new genus, 

 Lestornis (Z. crassipes), the remains of which indi- 

 cated a large swimming bird, fully six feet in length 

 from the bill to the end of the toes. 



" The Metamorphic Rocks surrounding the 

 Land's-End mass of Granite" is the title of a 

 recently-published paper by S. Allport, Esq., F.G.S. 

 The author described the results of a microscopic 

 examination of certain metamorphic rocks surround- 

 ing the Land's-End granite, indicating the changes 

 produced by the intrusion of the latter upon clay- 

 slate and upon certain igneous rocks. The slates 

 in contact with granite become converted into tour- 

 maline and mica-schists, and are found to contain 

 crystalline quartz, tourmaline, and three distinct 

 varieties of mica, with occasionally tremolite, mag- 

 netite (and andalusite?), and in some localities 

 felspar. Their structure is also changed, the most 

 remarkable changes being foliation with every 

 gradation from nearly straight parallel lines to the 

 most complicated contortions, and concretionary 

 structure by segregation of quartz and mica, the 

 result being a spotted schist. The strata near the 

 granite contain far more quartz than those at a 

 distance ; and the author thought that there could 

 be no doubt that much of the quartz has been 

 derived directly from the intruded rock. He referred 

 particularly to the fluid-cavities contained in the 

 quartz of the granite, schorl-rock, and altered slates ; 

 and from his observations upon them, stated that 

 he was compelled to dissent from the views of Mr. 

 Sorby, inasmuch as he found no uniformity to pre- 

 vail in the relative sizes of the bubbles and fluid- 

 cavities in the quartz crystals belonging to pre- 

 cisely the same portion of rock, or even in the same 

 crystals. Hence he regarded it as impossible to 

 arrive at even an approximate estimate of either 

 the temperature or the pressure under which a 

 given rock was formed, from a consideration of such 

 characters. The author next described the charac- 

 ters and mode of occurrence of tourmaline both in 

 the granite and in the schorl-rock, and inferred that 



at the separation of the latter from the former the 

 whole mass was in a plastic state, and that then the 

 tourmaline and quartz became crystallized in an 

 order varying in accordance with varying conditions. 

 He also noticed the alteration of tourmaline pro- 

 ducing pseudomorphs of that mineral ; and stated 

 that while all the three varieties of mica found dis- 

 tinctly furnish the red lithium line when treated 

 spectroscopically, this is most strongly marked and 

 persistent in the white variety, which is probably a 

 typical lepidolite. The altered dolerites and basalts 

 described by the author in the remainder of his 

 paper are marked as " Greenstones " on the map of 

 the Geological Survey. They were stated to vary 

 in colour from dark bluish-green to dark brownish- 

 green, and in texture from coarsely crystalline 

 rocks, not fissile in any direction, to fine-grained or 

 compact rocks with an imperfect slaty cleavage. 

 The coarsely crystalline rocks are regarded by the 

 author as altered dolerites, and some, if not all, of 

 the more compact varieties as originating from fine- 

 grained basaltic portions of the same rocks. The 

 author was unable to decide whether these masses 

 are contemporaneous and interbedded or intrusive 

 sheets ; — both may be present, but in any case they 

 are older than the granite. He described in some 

 detail the structure of specimens of these altered 

 rocks from many localities, the microscopic exami- 

 nation of which shows that the pyroxenic mineral, 

 whether augite or diallage, has frequently been con- 

 verted into a hornblendic substance, and that 

 actinolite is found filling cavities and fissures in 

 precisely the same manner as other products of 

 alteration. The imperfect cleavage of the more 

 compact varieties is regarded by the author as in 

 accordance with the facts observed in typical slates. 

 The metamorphism of the dolerites is regarded by 

 him as different in kind from that of the slates, and 

 caused rather by a decomposition and rearrange- 

 ment of mineral substances in situ than by an intro- 

 duction of new material. In many cases the process 

 of alteration may be followed step by step ; and 

 from the evidence it would appear that two rocks 

 of similar origin and composition may follow two 

 different lines of metamorphosis, and thus become 

 converted into two totally different substances ; and 

 again many of the metamorphic rocks have under- 

 gone a second series of changes, brought about 

 chiefly by chemical forces, and indicated by the 

 occurrence of micaceous and chloritic pseudomorphs 

 after tourmaline and an alteration (hydration) of 

 the mica. With regard to the origin of the granite 

 of Cornwall, the author said that neither observa- 

 tion in the field nor microscopical study lends any 

 support to the notion that it is a metamorphic 

 rock ; but, on the contrary, that there is the clearest 

 evidence of former deep-seated volcanic action, in 

 the disturbance and alteration described in his 

 paper, and in the enormous number of granitic and 



