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HARD WICKE'S SCIENCE- G OSS IP. 



GEOLOGY. 



Table of Rocks. — We have received the third 

 edition of a table of superposition of British rocks, 

 showing the systems, formations, groups of strata, 

 characteristic rocks, prevalent minerals, and typical 

 fossils, by Mr, Thos. A. Readwin, F.G.S., &c. The 

 table is published, at one shilling, by Messrs. Spon. 



The Geology of Madeira. — At a recent 

 meeting of the Geological Society, a paper on this 

 subject was read by J. S. Gardner, Esq., F.G.S. 

 Madeira consists almost wholly of sheets of basaltic 

 lava of variable thickness, interstratified with tuff 

 scoria and red bole, cut by innumerable dykes. In 

 the central part of the island is a horseshoe-shaped 

 valley, more than 4 miles in diameter, its bed 2500 

 feet above the sea, its precipitous walls full 3000 feet 

 high, rising here and there to yet greater elevations, 

 and forming a central point in the mountain system 

 of the island. This the author regards as the basal 

 wreck of a volcanic mountain, blown into the air by 

 an explosion of exceptional violence. Fragments of 

 the slopes of scoriae which once composed the inner 

 shell remain on the peaks surrounding this amphi- 

 theatre. The Vlykes here are trachyte. The author 

 ■describes a limestone exposed in one place beneath 

 the basalts, and referred to the Upper Miocene, and 

 a plant-bearing bed associated with them, containing 

 fossils of species still living in the island, some of 

 which have been wrongly referred to extinct forms. 

 In conclusion the author remarked upon the almost 

 infinite variability of the genus Riibiis, and the 

 tlifficulty of distinguishing its species. 



Fossil Trees.— In Science-Gossip for March, 

 there were some notes on fossil trees which had been 

 found in some parts of America, and on reading them 

 I thought the following particulars might be of some 

 interest to your readers. During the last month we 

 have uncovered three large fossil trees in our marl 

 works, and I have taken the following measurements. 

 a. 6 feet high, 2 feet diameter at top and 3 feet 6 

 inches at bottom, b. Short stump 2 feet high, 2 feet 

 7 inches diameter, r. 18 feet long, and about 2 feet 

 to 2 feet 6 diameter. I enclose you a photo of the 

 one a, to which I will refer shortly. These are not 

 the only sj^ecimens we have unearthed, for since the 

 year 1869 we have been continually bringing them to 

 light after their long burial. In the above year, J. E, 

 Davis, Esq., read a paper before the North Stafford- 

 shire Naturalists' Field Club in which he described 

 the one then uncovered as a " Calamite," but since 

 then Mr. J. Ward, F.G.S. , has read two papers before 

 the same club in which he says, " The fluting on the 

 stems of the trees were characters not usually found 

 on the stems of Calamites, but that such markings 

 were characteristic of Sigillaroid trees." Altogether 

 we must have found some dozens, and below I give 



you the measurements of thirteen (in addition to the 

 three given above) which were taken by Mr. Ward. 

 These trees occur in one bed or stratum of marl, and 

 in that particular bed the marl is marked very much 

 with the imprints of ferns, and different vegetation, 

 it also contains many fossils of parts of Calamites, 

 and altogether gives a good idea of how prolific the 

 coal-period must have been in vegetation. The in- 

 sides of the trees have certainly been hollow, although 

 in most cases they are completely petrified, but the 

 stone of which they are composed contains very 

 numerous traces and marks of vegetation and ferns, 

 as if they had fallen in and become petrified with the 

 mud, &c., M'hich filled up the hollow of the plant. 

 On one occasion my brother found the fossil form of 

 some kind of fruit or nut in the centre of one of the 

 trees, but unfortunately it has been lost. In the 

 centre of the tree marked a there was a distinct 

 branch of some kind, about 3 feet long by 2 or 3 in 

 diameter, and which ran diagonally down the stem of 

 the tree, the bark of which was carbonised, but 

 which showed longitudinal and other markings very 

 distinctly. These trees from their position are 

 evidently in situ, as they stand at an inclination of 

 about 15 degrees from the perpendicular, which 

 corresponds with the "dip" of the strata in which 

 they stand. 



Hanley, Staff'. 



W. Hampton, F.C.S. 



The Crag Shells of Aberdeenshire and 

 the Gravel Beds containing them. — Another 

 paper on the above subject, of a very important char- 

 acter, was also read at the same meeting, by Mr. 

 Thomas F. Jamieson, F,G.S. The author, in i860, 

 described beds of sand and gravel on the coast of 

 Aberdeenshire, containing numerous fragments of 

 Crag shells. His subsequent studies have enabled 

 him to throw much further light on these shells and 

 their mode of occurrence. The deposits containing 

 the shells are almost wholly confined to the districts 

 of Slains and Cruden, and extend up to heights of 

 225 feet above the present sea-level. They generally 

 consist of coarse gravel with large subangular stones 

 up to 2j feet in length, intermixed with sand and 

 muddy materials ; the whole form ridges, like eskers 

 or moraines, though glacially striated blocks are rare 

 in them. The author describes the coast-section in 



