290 C. H. Smyth, Jr. — Dikes of Alnoite at Manheim, N. Y. 



plate, rays had to penetrate the sheet of aluminium, a few 

 layers of paraffine and black paper, and 100 pages of the book. 

 Rontgen rays of intensity ordinarily met with in the laboratory 

 penetrate at once very much greater thicknesses of these mate- 

 rials- 

 Through the kindness of Mr. F. Blackmer and Mr. D. Rupp, 

 of Colorado Springs, the box was taken to the summit of Pike'& 

 Peak (elevation 14,14:7 ft.) and fastened by wires upon a roof 

 sloping southward. The box was left in that position from 

 June 27 to August 10. When subjected to the usual process 

 of development, the plate failed to show any action of rays and 

 presented a uniform surface, without traces of shadows from 

 the metallic strips. Another plate, similarly exposed from 

 July 7 to August 28 in Rosamont Park, near Pike's Peak, at 

 an altitude of 9200 ft., gave the same result. 



Thus even in high altitudes no evidence of the presence of 

 Pontgen rays in solar radiation was obtained. 

 Colorado College, Colorado Springs. 



Aet. XLIII. — I^ote on recently discovered Dikes of Alnoite 

 at Manheim, N. Y. ; by C. H. Smyth, Jr. 



The occurrence of alnoite at Manheim, N. Y., is of interest 

 both on account of the rarity of the rock, and because it is one 

 of several rather widely-scattered occurrences of basic intru- 

 sions cutting the Paleozoic rocks of Central New York. 



When described by the writer,^ some years since, the rock 

 was represented, so far as known, by a single dike, of very 

 limited dimensions. Recent blasting in the stream gorge, a 

 few rods above the old locality, has exposed another dike, and a 

 third one of small size has been found nearby. The latter 

 dike is precisely like the small one previously described, but 

 not so well exposed, as it lies in a very irregular fissure, from 

 which it has been deeply weathered out, the resulting excava- 

 tion being nearly filled with bowlders washed in by the stream. 



A similar fissure, but much larger, formerly existed where 

 the blasting has been done, and is now clearly seen to have 

 been formed by the weathering of a dike about six feet in 

 width. The rock of this dike bears a general resemblance to 

 that of the smaller dikes, but shows some decided variations 

 resulting from the greater size of the intrusion. At and near 

 the contact with the surrounding Calciferous, it shows small 

 phenocrysts in a very fine-grained groundmass. Toward the 

 center, however, it becomes quite coarse and inclined to granu- 



* This Journal, III, xliii, p. 322, and xlvi, p. 104. 



