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LXII. On the Composition of Chalk Rocks and Chalk Marl by 

 invisible Orgajiic Bodies: from the Observations of Dr. Ehren- 

 berg*. By Thomas Weaver, Esq^., F.R.S., ^F.G.S., 

 M.R.I.A., 4-c. ^c.f 



THE remarkable discoveries effected, and the new light 

 thrown on geology by the indefatigable researches of Dr. 

 Ehrenberg, during several years past, through the medium of 

 the microscope, particularly in respect of the Infusoria and 

 Polythalamia tribes, highly instructive and interesting as they 

 must be to all naturahsts, are especially so to the geologist, 

 since they open to him a large field of inquiry, eminently de- 

 serving of cultivation. To draw attention to this subject, which 

 involves no less than an investigation as to what extent minute 

 organic bodies, invisible to the naked eye, may have contri- 

 buted to the production of all limestone formations, whether 

 of an origin posterior or anterior to the epoch of the chalk, 

 descending thus in the series to the primary limestones, it ap- 

 peared to me that a sketch taken from a portion of the labours 

 of Dr. Ehrenberg might be not only useful, but especially ac- 

 ceptable to such geologists as may not be conversant with the 

 language of the original. I propose then, in the first instance, 

 to advert briefly to the earlier researches of Dr. Ehrenberg 

 concerning the Coral tribes in general, and those of the Red 

 Sea in particular:}:; and in the second, to present such extracts 

 from the Memoir, the title of which stands at the head of this 

 paper§, as may answer the purpose of a general view. 



At the instigation of the Royal Academy of Sciences of Ber- 

 lin ||, Dr. Ehrenberg and his friend, the late Dr. Hemprich, 



* Communicated by the Author. 



t With an Appendix touching the researches of M. Alcide d'Orbigny. 



I See in the Abhand. der Konig. Acad. d. Wissenschaften zu Berlin for 

 the year 1832:— 



1. Contributions to the physiological knowledge of the Coral animals in 

 general, and in particular of those of the Red Sea, with an attempt to clas- 

 sify them according to their physiological distinctions ; read 3rd March, 

 1831, with additions printed 1st Dec. 1833, pp. 225-380. 



2. On the Nature and Structure of the Coral Banks of the Red Sea, read 

 22nd March 1832; revised and printed in Feb. 1834, pp. 381-432. 



§ Ueber die Bildung der Kreidefelsen und des Kreidemergels durch un- 

 sichtbare Oraanismen, in the Transactions of the Royal Academy of Sciences 

 of Berlin, for the year 1838, read 20th Dec. 1838, and 18th Feb. 1839, 

 pp. 69-149. 



II See the Report read to the Academy by M. Air. von Humboldt on the 

 Travels ofDoctors Ehrenberg and Hemprich through Egypt,Dongola, Syria, 

 Arabia, and the Eastern declivity of the highlands of Abyssinia, in the years 

 1820-1825, conveying a clear idea of the arduous and extraordinary la- 

 bours of those gentlemen in all branches of Natural History: Berlin, 1826. 

 Dr. Hemprich fell a sacrifice to his exertions in Abyssinia, on the 30th of 

 June, 1825. 



