On the Organic Composition of Chalk and Chalk Marl. 443 



is instantly produced ; if antimony be in tlie mixture, a curdy- 

 white precipitate is obtained : if, on the contrary, neither 

 arsenic nor antimony is in the matter under exammation, the 

 hydrogen instantly reduces the silver of the test-liquor to the 



metallic state. , . , , • i ■ u 



It is really beautiful to see the admu-able manner m which 

 this test performs its duty, and I submit the same with 

 confidence to the attention of your numerous readers and 

 correspondents. 



I am, Gentlemen, yours truly, 



J. Marsh. 

 Royal Arsenal, Woolwich, May 10th, 1841. 



LXXIII. On the Composition of Chalk Rocks and Chalk 

 Marl by invisible Organic Bodies : from the Observations of 

 Dr. Ehrenberg. By Thomas Weaver, Esq., F.R.S., 

 F.G.S., M.R.I.A, Src. S'c. 



[Continued from p. 397-] 

 On the Geographical Distribution of Living Polythalamia on 

 the African and Asiatic Coasts of the Mediterranean, and in 

 the Red Sea. 



THE materials collected by Dr. Hemprich and myself in the 

 Mediterranean refer to four points on the Libyan coast, and 

 one point on the Syrian coast. In regard to a second point on 

 the latter coast (St. Jean d'Acre), I have acquired a knowledge 

 of some forms from the collection of Dr. Parthey. 



From the Red Sea nine forms were made known to us by 

 d'Orbigny, collected from sand presented to him by Deshayes. 

 But from the collections made by Dr. Hemprich and myself 

 from thirteen points along the whole length of the Red Sea, it 

 appears that very numerous forms exist. Of seven of those 

 points, one occurs on the western (African) coast at Suez, and 

 six on the eastern (Arabian) coast, namely, at Tor, Erraie and 

 el Ard, Moileh, el Wusch and Gumfude; and of the remain- 

 ing six, five are islands on the Arabian side, namely, Sanafer, 

 Maksure, Barkan, Sanac and Ketumbul, and one an island 

 on the African side of the Red Sea, namely, Massaua. 



It is possible that by repeated and closer exammation of the 

 marine productions collected by us, many other Polytlialamia 

 may be found besides those already discovered. In the mean 

 time, as a preliminary, I have drawn up a list of the species 

 iiitherto met with*. From this it results that the total num- 



• Of d'Orbigny s nine si)ccies from the Red Sea, there arc three which 

 I cannot identify, namely, TrUoculina bkurmala, Qumjucluadiua Imbala, 



