ANNIVERSARY ADDRESS OF THE PRESIDENT. IxXXvii 



calcareous beds against which they pressed were frequently fractured^ 

 and into the fractures the granitic matter was forced, forming the gra- 

 nite veins, as they have been termed, which can often be traced termi- 

 nating in somewhat fine threads ; so that not only was the pressure 

 great, but the fluidity of the igneous rock sufficient to pass into small 

 rents and cracks." He makes the following important remarks : — 

 " When we observe the mode in which the granites of Cornwall and 

 Devon have been brought into their present position, it is evident that 

 they have not been intruded in the mamier so common among the 

 trappean rocks in this region. We have nothing resembling the ac- 

 cumulations of ashes or cinders, nor the lines and masses affording 

 sections like those of upturned lava streams or sheets of matter ejected 

 from craters, and widely covering subjacent detrital or calcareous 

 accumulations * ." 



The following cases of metamorphic action and the observations of 

 the author upon them are highly interesting : — "Some of the changes 

 of the sedimentary deposits, effected by the heated molten rock in juxta- 

 position, have even amounted to a melting of such rocks and their con- 

 sequent incorporation, in part, with those in igneous fusion at the time. 

 There can be little doubt that detrital rocks, chiefly composed of fels- 

 pathic matter, have been so melted between two masses of greenstone, 

 greenstone porphyry, and vesicular trap, as to form one body with them, 

 their original bedded character appearing both on the north and south, 

 and the change from the one condition to the other being very gradual. 

 Great care is required, while studying this portion of country, not to 

 confound trappean substances with true fused rocks, since organic 

 remains are to be discovered m many beds which, at first sight, per- 

 fectly resemble those which have undergone fusion. Some colourless 

 argillaceous accumulations have become by metamorphic action large 

 natural beds of biscuit china, the elementary substances being the same 

 as a potter might employ for the purpose. Rocks of this class, though 

 not of the finer varieties, are seen to contain crystals of felspar, so as 

 to constitute a sort of porphyritic slate ; a kind of alteration shomng, 

 that the conditions attending it were such as to permit a movement 

 of particles ; so that some of the component elementary substances 

 could adjust themselves in a definite manner, and complete the crystal- 

 lization of the compound formed, while the remainder retained a coarse 

 porcellanic character, the body of the rock keeping the lamination due 

 to the original deposit of fine detrital matter from mechanical suspen- 

 sion in water f. 



There are many other observations throughout the work on chemical 

 action, exemplified in many of the phsenomena described, which are 

 very important, as leading to a more correct understanding of the true 

 nature of the rocks. I will give as examples those that relate to the 

 colouring matter of the greenish-blue bands and spots of the red-sand- 

 stones, and to the formation of clay-ironstones. A large extent of 

 country, in Herefordshire, Shropshire and South Wales, is covered 

 by the old red sandstone deposit. It is estimated that there is an 

 unbroken surface of 2100 square miles, and taking the average thick- 

 * Page 232. t Page 33. 



