156 Intelligence and Miscellaneous Articles. 



sea-bed. The littoral or marginal shingles of the lower cretaceous 

 series He towards the west ; that of the Lower Greensand is seen 

 in the Farringdon Gravels ; that of the Gault in the Halden Sands. 

 The Chalk proper filled up the deeper and subsiding sea-l)ed at a 

 period synchronous with the deposition of some of these littoral 

 beds, and at the time of the greatest extension of the area of the 

 Cretaceous Ocean, the littoral beds of which are recognizable in 

 the South of Norway and Sweden, in Westphalia and Rhenish 

 Prussia, &c., and the area of which probably may be regarded as 

 reaching from the Rocky Mountains at the head of the Missouri, 

 over Texas, Florida, the eastern side of the Alleghanles, the "West 

 Indies, and a broad belt of the Atlantic, to North Africa, Central and 

 Northern Europe, with bold extensions into Western, Central, and 

 even Eastern Asia. Central Europe then presented the aspect of 

 a huge archipelago from its many extensive islands, of which one 

 of the largest was an area comprising the chief part of France, 

 the north-east of Britain, Ireland, Norway, Sweden, Lapland, and 

 what are now the separating channels ; together with a part of 

 the Atlantic to the west and south. From the northern part of the 

 old land-area the author believes that the granitic boulder of Croydon 

 was derived. And, as it is, in his opinion, too massive to have been 

 transported by floating trees, as Mr. C.Darwin describes an Isolated 

 rock-fragment to have been conveyed to the coral-islands of the 

 Keeling group, — or by sea-weeds (the floating-powers of which the 

 author has studied in the English Channel), — Mr. Godwin-Austen 

 refers to an ice-floe as the agent by which such a block could alone 

 have been lifted from the coast and conveyed far out to sea. The 

 possible occurrence of rare and isolated boulders in the chalk-sea 

 under such conditions was analogous, in Mr. Austen's opinion, to the 

 occasionally extended voyage of icebergs at the present day to the 

 coast of Ireland, the Azores, and even to the Madeira Islands. 



XXI. Intelligence and Miscellaneous Articles. 



THE TELESTEREOSCOPE. 



To the Editors of the Philosophical Magazine and Journal. 



11 Rose Street, Edinburgh, 

 Gentlemen, Jan. 12, 1858. 



ALLOW me to call your attention to the fact that Professor 

 Helmholtz's Telestereoscope, described in your last Number, 

 is essentially the same as the Pseudoscope (the exaggerating form 

 of it), my description of which appeared in your Number for June 

 1853. This is no doubt another instance of what so frequently 

 happens — two persons independently studying the same subject 

 arriving at the same result. 



Professor Helmholtz's instrument being designed for viewing 

 distant objects, he gives a very cursory statement of its effects 

 when directed to near ones, — and, if I understand it aright, not 



