392 M. Keilhau's Theory of Granite and other Hocks. 



pact limestone, even with its petrifactions, converted into light- 

 coloured crystalline marble; he will at the same points see 

 clayslate altered to flinty slate or striped jasper, and he will 

 observe that these changes proceed farthest where there is an 

 immediate contact with granite or syenite, but that they be- 

 come less and less considerable the more remote the point from 

 these rocks ; finally, he will also meet with a multitude of con- 

 tact minerals at the same boundaries, such as copper and iron 

 ores, calcareous spar, garnet, &c. We have said that these 

 phenomena are to be found in great abundance, but the ex- 

 pression ought rather to have been, that they here exhibit a 

 more striking development than at any other known locality ; 

 the altered strata have been here acted on by contact with the 

 granite, to the hitherto unexampled distance of one-sixth of a 

 Norwegian, or one-fifth of a geographical mile, that is to more 

 than one English mile. As to what relates to the contact pro- 

 ducts, it will be sufficient to mention, that of about sixty iron 

 mines, setting the smaller experimental workings out of consi- 

 deration, which occur in the granite and stratified districts of 

 the Christiania territory, there are twenty of them to be found 

 immediately at the boundaries of these two districts, and about 

 half as many in the tracts near the boundaries, where the lime- 

 stone and slate have undergone changes by contact with granite. 

 Porphynj toithout Qiiartz ; Amygdaloid and Basaltic for ma- 

 tions. — We proceed now to speak of another group of these 

 massive rocks. As granite and syenite are, geognostically 

 speaking, mere unessential modifications of one principal type, 

 so in this case, when taking only a general view, the black por- 

 phyries, or, as we may better express it, the porphyries without 

 quartz (guartsluse jjorpliyrer), the amygdaloids, and the ba- 

 saltic formations, are to be regarded as one group. They 

 compose along with that porphyry-conglomerate, which is also 

 to be ranked among the massive formations, two or three re- 

 ciprocally similar districts, all of which in every place present 

 the same relations to the other geognostical districts and moun- 

 tain-rocks of the territory. These porphyry districts, as we 

 may call them for the sake of brevity, are not much less exten- 

 sive than the granitic as to the area they occupy ; but their 

 masses are much more superficial than those of the granite, and 



