160 Scientific Intelligence. 



New York, and therefore have almost the dignity and value of 

 types. 



Of the specimens described and illustrated in the quarto vol- 

 umes of the Palaeontology of New York, the Museum possesses 

 two-thirds of those in volume i, covering the Cambrian and 

 Lower Silurian systems ; nearly eight-tenths of those in volume 

 ii, extending from the Medina to the Onondaga stages, inclusive; 

 three-fourths of those in volume iii, which treats of the Lower 

 Helderberg and Oriskany Groups ; more than one-third of those 

 in volume iv, which describes the Brachiopoda of the Devonian 

 system from the Upper Helderberg to the Chemung ; about 

 thirty per cent of the specimens illustrated in volume v, part i, 

 which is devoted to the Lamellibranchiata of the Upper Helder- 

 berg (or Corniferous), Hamilton and Chemung Groups ; and a 

 nearly equal proportion of the Cephalopoda and Gastropoda 

 illustrated in volume v, part ii. The collection, however, con- 

 tains only about 74 of the specimens of Bryozoa given in vol- 

 ume vi, and about 70 of the Crustacea illustrated in volume vii 

 of the Palaeontology of New York. Much of the material for 

 volume viii, on the Brachiopoda, was prepared for publication 

 prior to 1876, hence a large proportion of the specimens used for 

 illustrations are to be found in the American Museum, especially 

 of those used for the plates bearing the name of R. P. Whitfield. 



There are in this Department of the Museum 8,345 type and 

 figured specimens, representing 2,721 species and 190 varieties." 



2. The Laccoliths of the Black Hills ; by T. A. Jaggar, Jr. 

 with chapter on Experiments illustrating Intrusion and Erosion; 

 by Ernest Howe. 21st Ann. Rep. U. S. Geological Survey, 

 Part III, pp. 163-303. Washington, 1901. — This paper presents 

 the results of a careful and detailed study and mapping of the 

 igneous intrusions in the northern Black Hills in South Dakota 

 and Wyoming. A large number of laccolithic bodies are described, 

 aided by maps and cross sections, and their geologic relations 

 and mode of occurrence deduced. The subject is presented 

 chiefly from the structural and dynamical side. From the facts 

 thus presented the author derives a number of interesting and 

 important conclusions regarding the formation of igneous masses 

 of laccolithic character in sedimentary strata. He points out 

 especially the importance of orogenic disturbances and deforma- 

 tions in promoting their origin. He also gives interesting studies 

 showing the results of the gradual dissection by erosion of domed 

 uplifts produced in this way. The whole constitutes a notable 

 contribution to the literature on igneous intrusions. 



In the chapter by Dr. Howe are given the results of experi- 

 ments in which molten wax was forced upward from below into 

 a mass of previously prepared sediments. The uplifts thus made 

 simulate in all important particulars those seen in laccoliths, as 

 shown in the photographs of the dissections. The erosion pro- 

 duced by a rain of fine spray shows results much like those seen 

 in nature. The chapter as a whole is an interesting addition to 



