366 Scientific Intelligence. — Geology and Mineralogy , 



sufficient number of old and generally inaccurate observations. The 

 result shews the necessity for such a revision, and in addition to 

 errors of places in right ascension and declination, there are as many 

 in the estimation of the magnitudes of the stars. 



The difference between the magnitudes given by La Caille, and 

 those observed by himself lately, appears to have given Captain 

 Gilliss, U.S.N., (now conducting the American astronomical expedi- 

 tion to Chili), the idea, that there must be greater number of variable 

 stars in the southern hemisphere than in the northern ; but when 

 we consider the haste with which La Caille' s observations were made, 

 the imperfection of his instruments, the number of errors detected 

 by Mr Maclear in his places, and the frequent entry as a star of what 

 is undoubtedly a nebula, or a cluster of stars, and sometimes a very 

 loose and straggling cluster, — we cannot allow that any proof has been 

 made out of such a physical difference between the stars of the south 

 and the north. 



And with regard, too, to the supposed difference between the 

 shape of the world in the two hemispheres, which appeared from La 

 Caille' s measure of an arc of the meridian at the Cape, — ^Mr Maclear's 

 repetition and extension of that operation has, in an approximate cal- 

 culation, completely negatived that supposition ; and the more exact 

 computation of the great work is meanwhile being rapidly pushed on, 

 and will be received on its completion as a most precious addition to 

 our knowledge of the real figure of the earth. 



SCIENTIFIC INTELLIGENCE. 



GEOLOGY AND MINERALOGY. 



1. Reptilian Footprints in the Lowest Silurians. — Mr Logan who 

 has conducted so well the geological survey of Canada, at present in 

 London, a few days ago unpacked a case containing a series of slabs 

 and casts exhibiting impressions of footsteps and trails in the Pots- 

 dam Sandstone, the lowest fossiliferous bed of the Lower Silurian 

 or transition class of rocks hitherto reached in America. We are in- 

 formed these very interesting specimens have been seen and examined 

 by one of the most distinguished palseontologists of this country, who 

 considers them as Reptilian ; in all probability of an animal allied 

 to Emys. Thus we have indications of air-breathing vertebrates at 

 the first dawn of animal life. 



2. Map of Iceland. — The hydrographical surveys of the en- 

 trance of the Cattegat, and of the Great Belt, have been com- 

 pleted ; but the recent war with Prussia has delayed the contem- 

 plated examination of the west coast of Iceland, and other im- 

 portant works. However, the large map of this interesting island 

 has been completed, and a copy has been promptly forwarded to 



