ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 457 



of Sigillaria, Catamites, Lepidodendron and Ferns; some of tbc 

 species ranging from the Millstone grit into the Upper coal for- 

 mation, while others seem to be more narrowly limited. It is to be 

 observed, however, that as we leave the central part of the system, 

 the total number of species diminishes both above and below, and 

 that it is only in those beds which hold large numbers of plants in 

 situ or nearly so, that we can expect to find a great variety of 

 species, and especially the more delicate and perishable organisms. 

 It is also quite observable in the Joggins section that while some 

 beds, in the same part of the system, supported Sigiltarice, others 

 carried Catamites, others mixtures of these with other plants; so that 

 differences of soil, moisture, etc., frequently cause neighbouring 

 beds to be more dissimilar in their fossil contents than others much 

 more widely separated. These local and temporary differences 

 must always have occurred in the deposition of the coal measures, 

 and should not be confounded with those general changes which 

 are connected with lapse of time. 



Art. XXXI — On the Origin of Eruptive and Primary Rocks ; 

 by Thomas Macfarlane. Part III. 



III. The Primary Formation. 

 Following out the plan indicated in the first part of this paper, 

 >we proceed to the consideration of the primary rocks, with the 

 view^of ascertaining whether they, in part at least, may reasonably 

 be regarded as constituting the first solidified crust of the earth. 

 The igneous condition of the original globe has already been ad- 

 verted to, and it would seem unnecessary here to refer at length to 

 what may be called the keystone of this theory, viz. the flattening 

 of the earth at the poles. It is sufficient to remark on this point, 

 that Newton and Huygens first maintained and proved this to be the 

 t<case, from mathematical grounds alone. Subsequently numerous 

 measurements of the length of a degree in various lands, but es- 

 pecially in those near the equator and under the polar circle, have 

 thoroughly established the truth of Newton's theory. They have 

 proved that the length of a degree of latitude increases with the 

 distance from the equator. The following are some of the results 

 obtained : 



Peru 



India 



France 



England 



Lapland 





Length of decree of 



Latitude. 



Latitude. 



1°31 



56736.8 toises. 



12°32 



56762.3 " 



46 Q 8 



57024.6 " 



52°2 



57066.1 " 



62°20 



57196.2 " * 



* Muller's Kosrnische Pbysik, p: 51. 



