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Dr. Boase begins by describing the composition and relation of 

 the several Primary Rocks, combining the accounts of geologists in 

 various parts of the world with the results of his own laborious in- 

 vestigations in Cornwall. I regret, that within the limits to which I 

 am restricted, it is impossible forme to do justice to the merits of 

 this important work ; I must confine my observations to a few of its 

 most characteristic features. Dr. Boase is of opinion that the con- 

 nexion between Unstratified and Stratified Rocks shows that they had 

 a common and contemporaneous origin. He observes that granitic 

 masses are as complex in their composition as stratified rocks, and 

 form sometimes distinct regular beds, highly inclined and alternating 

 with one another; that the elvans, or insulated beds of granitic rock, 

 always partake of the nature of the containing slate, and have the 

 same basis ; that the difference between the granite and killas, or 

 elvan, in Cornwall is often feebly marked, and still more feebly the 

 difference between the granite and gneiss of Scotland and Germany^ 

 as little difference is there between the granite of the Alps and the 

 talc slate adjoining. Where the granite changes its character, a cor- 

 responding change, he says, takes place in the slate. The elvans 

 are connected on either side with the granite they intersect by the 

 most intimate mineral gradations, or contain irregular portions or 

 masses of the common granite, with which they coalesce ; both 

 are penetrated by crystals of felspar ; both are striped with shorl. 

 At Pednimerer Meer one of the parallel layers of granite runs 

 through the elvan. In Scotland different beds of granite will inter- 

 sect a common mass, and pass by minute mineral transition into one 

 another, or into the characteristic granite of the district. 



Dr. Boase considers that the Primitive Shisti are improperly said 

 to be stratified. Pini has expressed the same opinion in two sepa- 

 rate memoirs; the supposed planes of stratification are, in his view 

 of the subject, mere transverse fissures. Prof. Phillips, Mr. Scrope, 

 Dr. Fleming, Prof. Sedgwick, have all felt and expressed the dif- 

 ficulty of distinguishing in these shisti planes of cleavage, and planes 

 of stratification. In the days of my geological apprenticeship I took 

 great pains to observe and record dip and direction, and fondly 

 hoped to obtain so large a number of accurate data on this subject 

 as might enable me to arrive at last at some general and impor- 

 tant result. I threw these data into tables, which only bewildered 

 me. Suspecting the accuracy of my early observations, I re- 

 peated them again and again, guarding myself on every occasion 

 more and more against probable sources of error; still I found my 

 results perpetually varying, till at last my patience was exhausted, 

 my Clinometer discarded, my registers destroyed. Let it not be 

 supposed, however, that my observations were useless ; they taught 

 me a salutary distrust. 



• Dr. Boase remarks that all the Slate rocks are composed of rhom- 

 boidal concretions, which are developed on a large scale by disinte- 

 gration. Mr. Scrope had anticipated this remark, and generalizes it. 

 He says the stratification of rocks of all kinds, where the strata are 

 separated by seams, is produced by concretionary process. 



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