Ailing — Problems of Adirondack Precambrian. 65 



conservative to have chosen a more local name than 

 "Algoman," yet Cushing has proposed a term in 

 "Laurentian" which has from time to time possessed 

 different shades of meaning. The writer does not claim 

 that the term Algoman as applied to the later series of 

 eruptives is original with him. He has heard it used in 

 the field, perhaps more commonly by St. Lawrence 

 county geologists. The Precambrian rocks of Canada 

 have been studied in sufficient detail to furnish data for 

 numerous correlation tables, twenty of which have been 

 examined. There is a striking similarity in nearly all; 

 there are only two periods of igneous activity prior to 

 the Keweenawan. The old granite is regarded as Lau- 

 rentian, hence, if we follow W. G. Miller and Knight 37 we 

 are, perhaps, compelled by the force of circumstances to 

 employ the term Algoman; it furnishes a much desired 

 1 < handle.' > 



The Gabbroic Dikes. 



The writer has encountered several dikes, usually only 

 3 to 4 feet wide, that are of peculiar composition. They 

 are strikingly equigranular and composed of labra- 

 dorite, augite, garnet and magnetite. Sometimes horn- 

 blende and biotite occur in addition. Mineralogically 

 they can be classed as gabbros but no diabasic or gab- 

 broic texture is visible even under the microscope. One 

 occurs at Euba Mills, in the Elizabethtown quadrangle, 

 another a mile south of the town of Saranac Lake on the 

 shore of Lake Flower, a third one was seen on the Blue 

 Ridge-Newcomb road in the Schroon Lake sheet. Still 

 another occurs at the eastern entrance of the Gulf, in the 

 Ausable sheet. In each case they are cutting anorthosite. 

 Undoubtedly more will be encountered as field work is 

 continued. 



Diabase and Trachyte. 



On the Faxon Graphite property, Bolton quadrangle, 

 Mr. D. H. Newland pointed out to the writer a diabase 

 dike which has assumed a most peculiar form. It is of 

 normal Adirondack diabase, olivine free. Instead of 

 behaving like the rest of the dikes of the region it has 

 failed to reach the surface, expending its energies in the 

 formation of a laccolithic body some 300 feet long and 25 

 feet thick. It splits the " Dixon' ' schist into two seams. 



87 Miller, W. G., and Knight, C. W. : Jour. Geol., 23, p. 588, 1915. 



Am. Jour. Sci.— Fourth Series, Vol. XLVIII, No. 283.— July, 1919. 

 5 



