GEOLOGY OF THE LAKE PLACID QUADRANGLE 63 



About one-half of a mile northeast of the summit of Catamount 

 mountain, a diabase dike 3^ feet wide sharply cuts the largest 

 gabbro-diorite dike obliquel}^ and the granite parallel to its folia- 

 tion. A few rods farther east there are five dikes, none over a few 

 feet wide, and roughly parallel. 



Near the summit of Catamount, a dike (no. 52) 6 feet wide may 

 be clearly seen cvitting the granite for several hundred feet. This 

 may be a continuation of the large dike (no. 51) one-half of a 

 mile to the northeast. 



On the mountain top i}4 miles northeast of Catamount summit, 

 there are several dikes from 2 to 6 feet wide, nearly parallel, and 

 close together. 



Dikes nos. 13 and 53, each about a foot wide, sharply cut gabbro 

 stocks. 



Dikes nos. 3, 30 and 35 show various branches or tongues extend- 

 ing into the country rocks. No. 3 is in contact with a pegmatite 

 dike, and it is considerably brecciated due to faulting. 



Dike no. 55, one-half of a mile north of Franklin Falls, is 2 feet 

 wide. It contains fresh labradorite crystals as phenocrysts up to 

 an inch long with very evident twinning bands. 



Very instructive dikes may be seen at locality no. 28 where sev- 

 eral dikes (one 10 feet wide) sharply cut Whiteface anorthosite. 

 There were very plainly two injections of diabase magma here. The 

 earlier injected mass was the larger, and it solidified into a dark 

 bluish gray rock with a very fine-grained diabasic texture. The 

 second injected masses are only a few inches wide, in sharp con- 

 tact with the first ; black and almost glassy with very small pheno- 

 crysts of labradorite \A'hose long axes are approximately parallel 

 thus causing this second intrusive to have a fairly good flow-struc- 

 ture. A similar combination of diabase cutting diabase was 

 observed in a glacial boulder i mile southeast of Wilmington. 



Dike no. 42 (see no. 63 of table 6) is only 4 inches wide, but it 

 exhibits a very fine diabasic texture in the middle portion, and 

 black glass at the margins. 



At locality no. 18 several dikes from 5 inches to over 5 feet wide 

 are close together and sharply cut Grenville quartzite. 



In the old limestone quarry at dike locality no. 16, a good diabase 

 dike with several small branches sharply cuts the limestone. 



The Rocks of Catamount Mountain 



A remarkable assemblage of rocks occurs within an area of less 

 than I square mile, including the summit and southern base of 



