OEIGIN OF CEYSTALLINE EOCKS. 13 



were disintegrated by coming in contact with water while in a fused condition, or (3) 

 were broken by abrasion after consolidation. In any case, the detrital matter, as in 

 the Hvittoniau hypothesis, was supposed to be transformed into a crystalline rock by the 

 action of heated waters. 



§ 26. After assigning such an origin to certain rocks called by him metamorphic por- 

 phyries and basalts, with regard to which he supposes " every eruption produced a heated 

 sea around it, which hardened " the disintegrated porphyry, and recrystallized the commi- 

 nuted materials, Dana proceeds to say that " granite, like porphyry, is an igneous rock. In 

 its era, granite-sands were formed like porphyry-sands, and restored by heat to metamorphic 

 granite, like metamorphic porphyry. . . . I use the word granite here as a general term 

 for this and the associated rocks, mica-slate, syenite and hornblende-slate, etc., which, I have 

 shown, may also have an igneous origin. These granite-sands, like porphyry-sands, were 

 formed about the regions of eruption, in one of the modes pointed out, and in all proba- 

 bility were never clays like the alluvial deposits of the present day With regard to 



primary limestones, a general survey of the facts seems to evince that some of these were 

 of igneous origin like granite. If this were the case, there must have been others, 

 formed at the same time with the deposits of gi-anite-sand, and through the action ot 

 the same causes. These were recrystallized by the next discharge of heated waters." -' 

 Dana, forgetting the effects of the law of convection in liquids, here makes the sug- 

 gestion that "at no great depth the waters might be raised to the heat of ignition 

 before ebullition will begin, and if the leaden waters of a deep ocean ... are for days 

 in contact with the open fires of submarine volcanoes, we can scarcely fix a limit to the 

 temperature which they would necessarily receive." 



We have thus presented a complete exoplutonic or volcanic hypothesis, and at the 

 same time a complete metamorphic or A^olcanic-detrital hypothesis, alike for porphyry, gra- 

 nite, syenite, gneiss, mica-schist and crystalline limestone ; each and all which are 

 assumed to have a two-fold origin, and to appear alike in an eruptive and in a secondary 

 sedimentary form. A reference to the previous speculations of Scrope, already set forth in 

 § 1*7, will show to what extent Dana was his disciple. 



§ 2Y. Dana has since abandoned this hypothesis, so far as regards the eruptive origin of 

 the detrital matters. In his later writings, he sets forth the familiar view of a liquid interior 

 covered with a solid crust, which latter was the supposed source of the Archœan or 

 primitive rocks. " These Archaîan rocks are the only iini versai formation ; they extend 

 over the whole globe, and were the floor of the ocean, and the material of all the emerged 

 land, when life first began to exist." These rocks of the first crust, disintegrated by sub- 

 marine and subaërial agencies, yielded beds of detritus, which, being consolidated by the 

 action of the heated waters, gave rise to new rocks, which would " be much like those 

 that resulted from the original cooling, because chiefly made out of the latter by re-conso- 

 lidation and re-crystallization." " Igneous rocks have a close resemblance to granite, 

 diorite, and other crystalline kinds, and hence may have proceeded from the fusion of 

 older kinds. But these older kinds derived their material from an older source, and 



^' Dana, On the Analogies between the Modern Igneous Rocks and the so-called Primary Formations. Amer. 

 Jour. Science, 1843, vol. xlv., p. 104-129. 



