1832.] Progress of Mechanical Science. 425 



two groups, the " great scar limestone" is the lower, having an average thickness 

 of more than 500 feet, and containing orthocerata, trilobites, and ammonites. The 

 younger group contains five beds of limestone, of which the highest or " 12 fa- 

 thom limestone" is associated with many strata of sandstone and shale, and 3 or 4 

 seams of workable coal. The whole of this calcareous system is overlaid by a 

 complex group connected with the millstone grit, and interlaced with beds of shale, 

 and one or two seams of coal. From his general conclusions we learn, that the 

 carbonaceous formations become much more calcareous in their range to the 

 north — that from the nature of the associated organic remains, coal has, in some 

 places, been produced in deep seas, and in other places in shallow estuaries, — that 

 changes in the mineral character of tlie contemporaneously formed strata are usu- 

 ally accompanied by changes in the species of the fossils, whether animal or vege- 

 table — and lastly, that the valleys in the carboniferous chain, near the lines of sec- 

 tion, are not fissures which have been deepened by erosion, but true valleys of 

 denudation. 



13. Correction of a mistake in the notice on Marine Surveys. 



In page 333, line 4, where mentioning, that the sextant is used for taking the relative 

 positions of points on shore, it was said that " the azimuth compass was resorted to only 

 for laying down the true meridian." Every surveyor will see, that this must be an inac- 

 curacy, as such determinations would ill accord with the exactitude obtained by the other 

 parts of the operation. The sentence should have run thus ; — " azimuths taken with the 

 sextant between the limb of the setting or rising sun and some fixed object on the 

 horizon, as an island or peak, afforded the means of determining the true meridian." 

 Such we know to be the method practised by Captain Ross. 



VII. — Progress of European Science. 



Mechanics. 



1. Steam Carriages. 



The introduction of steam carriages on the turnpike roads of England may now be 

 considered as established : this grand improvement has broken its way through the 

 difficulties opposed to it — in the nature of the machinery, — the varying resistances 

 and levels of the roadway,— the prejudices of the public against its dangers and incon- 

 veniences, and the strenuous opposition of the stage-coach proprietors, and of the 

 toll trustees, whose prohibitory increase of charge has been finally levelled by an 

 Act of Parliament, if not passed, at least brought up by the chairman of the Select 

 Committee appointed to inquire into the subject of steam carriages, and conse- 

 quently not likely to be negatived. 



This great achievement in mechanics has prevailed through two irresistible 

 practical arguments : lst> journeys from London to Bath and Southampton have 

 been performed, and 2nd, a great saving of expence to travellers has been certified. 



The following extract from the " Report" shews the progress already made : 



" The first extensive trial of steam as an agent in draught on common roads, was 

 that by Mr. Gurney, in 1829, who travelled from London to Bath and back in 

 his steam carriage. He states, that although a part of the machinery, which brings 



2 h 2 



