Whilst the older trappean rocks have apparently had so much influence on the disturbance and fracture of the sedimentary strata older than the Carboniferous, and by a secondary process have evidently been centres of mineralising action, the volcanic seem to have played the most important part in determining the elevation and present physical outline of north-eastern Queensland. The main outbursts of lava have taken place along the Dividing Range which separates the eastern and western waters, and therefore on the line of the highest elevation of the country. The more northern volcanic areas, are probably contemporaneous with the upper volcanic series of Victorian geologists, so extensively developed in the western districts of that colony. These have issued from well-defined craters still in existence, and are probably of Pliocene Tertiary age. The southern areas, viz., Peak and Darling Downs, etc., are older, agreeing with the lower volcanic of Victoria, which have been ejected through fissures, and have in no case a very extensive flow beyond the lines of fracture through which they issued. These may be referred to the Miocene Tertiary epoch. The rock masses forming both the upper and lower volcanic are basic in character, and may be all termed or grouped under the general term "dolorites." The volcanic soils of Queensland are those best adapted for the grazier and agriculturist. To epitomise:--With the exception of the McKinlay Ranges, a line drawn parallel to the eastern coast, at a distance of 250 miles, would include all the palæozoic, metamorphic, granitic, trappean, and volcanic rocks represented in the colony, both coal groups lying within the same area. The mesozoic and cainozoic systems occupy the surface area to the westward. The volcanic rocks follow the line of greatest elevation on the main watershed at altitudes from 1,500 to 2,000 feet above sea level. The chief granitic mass extends from Broad Sound to Cape York, with an occasional capping of "Desert Sandstone." Westward from the Dividing Range, "Desert Sandstone" and the cretaceous and oolitic groups alternate one with the other to the extreme limit of the colony. AREA OF FORMATIONS. Estimating the entire extent of the colony at 600,000 square miles, a rough approximation to the areas occupied by the different geological formations is as follows:-- Square Miles. Valueless land, "Desert Sandstone" 150,000 Scrubby and thickly timbered inferior pastoral, { Carbonaceous } but valuable as containing { Mesozoic and } 24,000 coal, iron ore, &c. { Palæozoic } Fair pastoral, and valuable { Devonian } for its associated minerals { Silurian } 60,000 and metals { Metamorphic } Fair pastoral Granitic 114,000