556 British Association for the Advancement of Science. 



fossiliferous rocks well determined ; also that it not only sends veins 

 into them, but that it actually in some degree overlaps them, the 

 strata rather turning up from it. The granite sometimes becomes sy- 

 enitic, passing into trap porphyry ; and it has altered the appearance 

 of the adjacent rocks, making them truly metamorphic. These fossi- 

 liferous rocks rest upon gneiss, and may be referred to the Silurian 

 system of Murchison. The granite in the same vicinity comes in con- 

 tact with the gneiss, which rock has frequently indications of having 

 been disturbed before the deposition on it of the Silurian rocks, and 

 it bears on its surface marks of scoring and abrasion. The posterior 

 formation of the granite is proved by its veins in the adjacent rocks, 

 and by the fragments of gneiss in the Silurian strata. The entire 

 phaenomena are of the highest interest, — they must have been origin- 

 ally submarine, as the disturbances would have been vastly greater, 

 had they not taken place under a pressure of perhaps some miles of 

 ocean in depth, and perhaps also with other strata upon them : the 

 gneiss, under such a pressure may have been only softened. Near 

 Christiania, many dykes, evidently of volcanic origin, also occur; 

 these are of syenite passing into greenstone, and are evidently fissures 

 filled with injected matter. 



Section of Mechanical Science, Sept. 12. — Mr. Fairbairne then read 

 a report on the comparative strength and other properties of cast 

 iron, manufactured by the hot and cold blast respectively. 



At a previous meeting of the Association, Mr. Hodgkinson read a 

 report on the comparative strength and other properties of iron ma- 

 nufactured by the hot and cold blast. — In the prosecution of inquiries 

 since made, it was conceived desirable to subject the metals operated 

 upon to more than one species of strain j to vary theirforms, and, by 

 a series of changes to elicit their peculiar as well as comparative pro- 

 perties. First, they have been drawn asunder by direct tension. Se- 

 condly, they have been crushed by direct compression, both in short and 

 long specimens, (the results of which will be given in a paper read sub- 

 sequently) j and, Thirdly, they have been subjected to fracture by 

 transverse strain, under various forms of section, and at various tem- 

 peratures. Ten bars of hot and cold blast iron were also loaded with 

 different weights from 1 121b to near the breaking point, and left for 

 many months to sustain the load, and to determine the length of time 

 necessary to effect the fracture. The bars thus loaded, are still (with 

 one exception) bearing the weight, having been suspended up- 

 wards of six months, and from what we can at present perceive, there 

 is every chance of a long and protracted experiment. In making the 

 experiment on transverse strain, a number of models of different sizes 

 and forms were prepared, and the irons, both hot and cold blast, were 

 run into the form of these models ; but as there is usually a slight de- 

 viation in the size of the castings from that of the model, the dimen- 

 sions of the bars were accurately measured at the place of fracture, 

 and the results reduced by calculation to what they would have been 

 if they had been cast the exact size of the model, assuming the strength 

 of rectangular beams to be as the breadth and the square of the depth, 

 and the ultimate deflection to be inversely as the depth, the length 



