1873.] Geology. 545 



in being constituted throughout their whole thickness by alternations of 

 marine and estuarine series of beds ; in which respect they precisely resemble 

 the equivalent strata of Sweden. The Triassic rocks have now been dis- 

 covered in Sutherland, where their conformable relations to overlying beds, 

 containing a fine Liassic fauna, entirely confirms the conclusions concerning 

 their age, derived from Professor Huxley's studies of the remarkable reptiles 

 yielded by them in Elgin. Two new species of Brachiopoda, discovered by 

 Mr. Judd in the Upper Oolite of Garty, in Sutherland, are named by Mr. 

 Davidson respectively, Rkynchonella Sutherlaffdi, after the Duke of Suther- 

 land ; and Tercbratula Joassi, after the Rev. J. M. Joass. 



Physical Geology. — The Rev. J. M. Mello, in a sketch of the geology of 

 Derbyshire, touches upon the solvent power of water on the mountain lime- 

 stone as explaining the origin of its characteristic scenery. He considers that 

 the dales were in many instances originally caverns, which have been through 

 countless ages eaten away by the streams till at length the roofs have fallen 

 in, and in their turn have been for the most part carried away by the same 

 powerful agent. 



The Rev. O. Fisher, in treating of the formation of mountains, has attributed 

 the elevating force, which has raised mountain ranges, to the contraction of 

 the heated interior of the earth, and subsequent wrinkling of the crust so as to 

 accomodate itself to the diminished nucleus. In a recent paper, communicated 

 to the " Geological Magazine," he proves that if we suppose a stratum 500 

 miles thick, buried under 25 miles of crust, to have contracted since the crust 

 became rigid on the whole, as much as a slag would do in passing from a 

 fused to a devitrified state, this would give a mountain-range of something 

 under half a mile high on every hundred miles of surface. If only a part of 

 the area were disturbed the mountains would be higher. 



Mr. W. T. Blanford has drawn attention to the superficial deposits of Persia. 

 He described especially the desert plains of the interior of the country, the 

 paucity and scantiness of the streams, most of which terminate in salt swamps 

 and lakes, and the occurrence of vast slopes of gravel on the margins of the 

 desert plains, covering up the junction of the latter with the surrounding 

 mountains. The desert plains he regarded as in general the beds of ancient 

 lakes. 



Glacial Geology. — The Duke of Argyll, in his Presidential Address to the 

 Geological Society, while discussing the general opinion in regard to the 

 glaciation of the British Isles, remarked " that the history of geology, like the 

 history of other sciences, is the history of the prevalence of particular theories 

 at particular times — not generally to be wholly abandoned, but almost always 

 to be greatly modified." He had " a strong impression that the glacial theory 

 is now at about its maximum, and that, when all our valley-systems are 

 described as being nothing but magnified striae, we are pretty near the summit- 

 level of this particular excursion of the scientific imagination." 



Dr. Dana's observations upon the Glacial and Champlain Eras in New 

 England, go to show that the former was an era eminently of transportation 

 by ice, the latter one of deposition. He regards the Glacial period as of great 

 duration, and expresses the opinion that 1 foot a week was the average rate of 

 the movement of the ice, so that 10,000 years would be required to carry a 

 boulder 100 miles. In the northern part of New England, he estimates the 

 ice to have had a thickness of from 5000 to 6500 feet, and in the southern part 

 an average of 2700 feet. The pressure must have been immense — 6000 feet 

 corresponding to at least 300,000 pounds to the square foot ; the glacier as it 

 moved must have had tremendous power in abrading, and made boulders and 

 gravel in immense quantities. 



Mr. J. C. Ward has described the glaciation of the Northern part of the 

 Lake district. He maintains that there is no evidence that a great ice-cap 

 from the north ever swept over this district. The ice scratches trending along 

 the principal valleys, but sometimes crossing watersheds, indicate a great 

 confluent glacier-sheet, at one time almost covering a great part of the district, 



