Metamorphic Rockg. 121 



at intervals by certain combinations, are questions for the 

 solution of which we have as yet no data to lead us beyond 

 probable inferences. It was long ago observed, that when 

 dykes of basalt passed through sedimentary rocks, earthy 

 limestones were frequently changed into crystalline marble, 

 shales into flinty slate, argillaceous sandstone into jasper, 

 and bituminous coal into graphite or cinder. Similar changes 

 were also often observed at the junctions of granite with se- 

 dimentary rocks. An attentive observation of these pheno- 

 mena led Hutton to infer, that the strata derived from the 

 detritus of pre-existing rocks had been consolidated into 

 stone by the agency of subterranean heat ; and although he 

 extended his theory to all the strata, to many which subse- 

 quent observations have shewn it to be inapplicable, still the 

 germ of the modem theory of metamorphism is clearly seen 

 in one of the fundamental positions of the Huttonian theory 

 of the earth. But sound as were the views of that philoso- 

 pher in his leading doctrines, they were adopted by a very 

 small number of geologists, so strongly had the theories and 

 system of Werner got possession of men's minds, especially 

 in Germany and France. About twenty years ago, however, 

 some startling facts were brought to light ; we heard that 

 Belemnites had been found in micaceous schists in the Alps, 

 and that an insensible passage could be traced from a se- 

 condary oolite full of organic remains, to the highly crystal- 

 line marble of Carrara, the old type of primary limestone, 

 and under circumstances which afforded the strongest pre- 

 sumptive evidence that the oolite had been changed into the 

 marble by the action of adjacent igneous rocks. Then there 

 came facts on a grand scale, analogous to those that had 

 been observed at the junction of trap dykes and granite veins, 

 with sedimentary rocks, and not only extending to great dis- 

 tances from the igneous rock, but the secondary shales were 

 changed into rocks that could not be distinguished from the 

 so-called primitive gneiss and mica-schists, and, like them, 

 included crystallized garnets. 



Mr Lyell, in 1833, brought forward a more extended and 

 complete development of the Huttonian hypothesis of conso- 

 lidation, and first proposed the adoption of the term •* meta- 



