Intelligence and Miscellaneous Articles. 285 



considered by some to be an extension of the zone of If . planus, the 

 form which marks the passage from the soft to the hard chalk. In 

 the remainder M. cor testudinarium was common (zone of M. cor 

 testudinarium) . 



Seen in thin sections under the microscope, the structure of the 

 hard beds which mark the limits of the Middle Chalk was stated to 

 be very similar. 



In conclusion, the author considered that the divisions of the Middle 

 Chalk, as set forth in the Cambr. Memoir, are well shown in the cliffs 

 of Dover ; but the hard beds which appeared to him the equivalent 

 of the Chalk Rock, and mark the upper limit of Middle Chalk, attain- 

 ing a great development at Dover, it became necessary to examine 

 the paheontological position of that bed to which the name " Chalk 

 Rock " was given by Mr. Whitaker. Having studied Mr. Whitaker's 

 description given in the ' Geology of the London Basin,' and having 

 examined exposures of this rock between Cambridge and the Thames, 

 he came to the conclusion that there was probably more than one bed 

 to which the name Chalk Rock might be applied, and that these, 

 probably not all persistent, may occur at different palasontological 

 horizons. He therefore proposed to take the zone of H. planus 

 as the top of the Middle Chalk ; although this zone was difficult to 

 identify inland, from the paucity of its fossils, the base of the over- 

 lying zone was well marked by the abundance of Mierasters and other 

 forms, which appeared to him more closely allied to Upper than to 

 Lower Chalk. 



He believed that while the Chalk Rock seen at Henley may be con- 

 sidered the summit of the Middle Chalk, the Chalk Rock of Cambridge- 

 shire, though convenient for marking the summit of the Middle Chalk 

 of that county, included that which was really the upper part of the 

 zone of II . planus and the base of the true Upper Chalk, the equiva- 

 lent of chalk with many Mierasters of Dover. 



He would therefore consider the Middle Chalk of Dover to be that 

 included from the base of the grit-bed to the summit of the zone of 

 H. planus. Its thickness was 242 feet at Shakespeare's Cliff. He was 

 indebted to M. Curry, Esq., of Dover, for this accurate measurement. 



XL. Intelligence and Miscellaneous Articles. 



ON THE VELOCITY OF EFFLUX OF LIQUIDS. BY M. VAUTIER. 

 HPHE experiments which lead to the determination of the velocity 

 -*- of efflux generally depend on a measurement of the quantity, and 

 on a coefficient of contraction of the jet. Bossut, however, verified 

 Torricelli's law by two experiments, in which he measures the 

 range of a horizontal jet of water (Traite elementaire d'Hydro- 

 dynamique, vol. ii. p. 120). 



In the course of researches on this subject, I have applied a 

 graphic method which enables me to measure directly the velocity of 

 efflux of liquids, and I have made use of this method for months. 



In the flat horizontal bottom of a cylindrical vessel full of water, 

 is an orifice in a thin plate, for which can be substituted an 

 ajutage. Inside the vessel and in the line of its axis is placed a 

 tube containing an emulsion of an insoluble liquid of the same 



Phil Mag. 8. 5. Vol. 21. No. 130. March 1886. X 



