800 



THE WONDERS OF GEOLOGY. Lect. VIII. 



be sufficient to state that the slate rocks almost universally 

 occur on the flanks of the primary masses, rising up into 

 lofty mountain peaks, and dipping beneath the newer sedi- 

 mentary deposits: thus Skiddaw, Sea- fell, Conist on-fell, 

 and Saddleback in Cumberland, peaks 3,000 feet high, are 

 slate rocks thrown up by a central mass of granite. 



The total thickness of the slate system, embracing under 

 that name all the deposits which intervene between the 

 Lower Silurian and the mica-schist, is much greater than 

 that of any other in the geological series, amounting to 

 many thousand yards. 



In Shropshire there is a group of the upper Cumbrian 

 rocks, unconformable to the overlying Silurian strata, 

 having evidently been thrown into highly inclined posi- 

 tions before the deposition of the latter. These rocks 

 by the primeval forests that fringe the coast, or where these have been 

 destroyed, by impenetrable thickets of esculent fern. The fundamental 

 rock is everywhere clay-slate, frequently traversed by greenstone dykes, 

 as at Port Nicholson, Queen Charlotte's Sound, and Cloudy Bay. On 

 the banks of the rivers Eritonga, Waibo, and along some parts of the 

 sea-coast, are horizontal terraces of boulders of trap-rocks, fifty feet 

 high. Anthracite coal crops out in the harbour of Wangarua ; and 

 there is a seam of the same mineral intercalated in hard grey sandstone 

 on the east coast of the Northern Islands. On the west coast of the 

 same, the limestone contains a few shells, Pecten, Ostrea, Terebratula, 

 and Spatangus. Veins of copper pyrites occur in the clay slate in the 

 great Barrier Island. The coasts are in many places fringed with recent 

 horizontal sediments consisting of loam, with fragments of wood and tree 

 ferns, &c. The small rocky islands of trachyte off the coast of the Northern 

 Island, also bear marks of wave-action to the height of 1 00 feet above 

 the present sea-level. In the interior of the Northern Island, there is 

 a lofty central group of volcanic mountains, some of the volcanoes being 

 still in activity; the ancient lava streams appear to have been prin- 

 cipally erupted from the base of the craters. The highest are Tonga- 

 riro 6,000 feet, (ante, p. 98) and Mount Egmont 9,000 feet high. The 

 loftiest summits are covered with snow. There are likewise many 

 lakes which appear to occupy ancient craters ; and numerous thermal 

 mineral springs, and a cold silicifying stream near Cape Maria." — 

 Dr. Dieffenbach, Brit Assoc, ifrp. 1845. 



