TREE RECORDS: GEOGRAPHICAL DISTRIBUTION 79 



figure 5, and gave as cycles: 9.3 (2), 18.8 (2, ■£■), and 34.8. So much 

 material was obtained subsequently from that area that this group, 

 with its informal treatment, has been retained as a check on the 

 others. Without doubt the Douglas firs could be included with the 

 yellow pines, but the Engelmann spruces should be kept separate. 

 This will appear in the Brook group of Engelmann spruce (BES) . 



PIKE'S PEAK TIMBERLINE GROUP (PPT) 



The first Pike's Peak group was obtained close to the Cog Road 



near timberline, at an approximate elevation of 11,500 feet. Naturally, 



the trees were not yellow pine. No. 1, a chip from a dead tree, had 



to be discarded, but five increment-cores, two in Engelmann spruce 



and three in fox- tail pine (Pinus aristata), proved good specimens. 



They were readily dated and were measured by Mr. Austin by the 



long-plot method. Each tree record was standardized and the curve, 



1734 to 1919, was smoothed in the usual way. The portion since 



1750 is given in figure 5. Its complacent character shows at once, 



yet it compares exceedingly well with the smoothed curves of groups 



3,000 feet lower down the mountain. The cycles are 11.7, 14.0, 20.0, 



22.6 (oc. J- or -J), and 37. This group, therefore, does not classify 



well as of Rocky Mountain type, but its cycles are of the general 



western sort. One notes here the tendency of the double sunspot cycle 



to fall a little below 23.0 years; in the Arizona area it was usually a 



little above. 



PIKE'S PEAK BASIN GROUP (PPB) 



In making its way east after passing timberline, the Cog Road 

 descends sharply into and then more gradually through a basin area 

 to an outlet in Ruxton Creek, where the water-supply for the cities 

 below is taken. The more level part of the basin has an altitude of 

 about 9,500 feet, and here four borings were taken, of which three 

 (PP 7 to 9) form the basin group. Mr. Austin measured these by the 

 long-plot method. After standardizing, a curve, 1693 to 1919, was 

 drawn and smoothed by graphic Hann; figure 5 gives the part since 

 1750. This has much larger variations than the timberline group and 

 compares closely with the later groups near the Alpine Laboratory. 

 The unusual feature in this group is the doubling of average growth 

 after 1865. The cycles are 10.2 (2), 13.0 (oc. |), 20.0 (3, £), 25.6, 

 and 30.7 (2, oc. ^ or £). The absence of a 17-year cycle is not 

 usual in this zone, but the presence of 25- and 30-year cycles is very 

 characteristic. 



UPPER NORTH TRANSECT GROUP (HNT) 



The Alpine Laboratory has an elevation of about 8,700 feet, and 

 near it are varying contours well worth testing. The various Pike's 

 Peak groups, including those already described, were originally 

 selected as a study in topography. After leaving the basin the Cog 



