The data are in "data frame" format, which are arrays of data in which each case (here an individual) corresponds to a row, and each variable corresponds to a column. The row labels for these data frames are just row numbers, the column labels are the names of the variables.
"Snow" <- structure(list(density = c(0.686, 0.686, 0.686, 0.686, 0.686, 0.686, 0.686, 0.686, 0.686, 0.686, 0.604, 0.604, 0.604, 0.604, 0.604, 0.604, 0.604, 0.604, 0.604, 0.604, 0.508, 0.508, 0.508, 0.508, 0.508, 0.508, 0.508, 0.508, 0.508, 0.508, 0.412, 0.412, 0.412, 0.412, 0.412, 0.412, 0.412, 0.412, 0.412, 0.412, 0.318, 0.318, 0.318, 0.318, 0.318, 0.318, 0.318, 0.318, 0.318, 0.318, 0.223, 0.223, 0.223, 0.223, 0.223, 0.223, 0.223, 0.223, 0.223, 0.223, 0.148, 0.148, 0.148, 0.148, 0.148, 0.148, 0.148, 0.148, 0.148, 0.148, 0.08, 0.08, 0.08, 0.08, 0.08, 0.08, 0.08, 0.08, 0.08, 0.08, 0.001, 0.001, 0.001, 0.001, 0.001, 0.001, 0.001, 0.001, 0.001, 0.001), gain = c(17.6, 17.3, 16.9, 16.2, 17.1, 18.5, 18.7, 17.4, 18.6, 16.8, 24.8, 25.9, 26.3, 24.8, 24.8, 27.6, 28.5, 30.5, 28.4, 27.7, 39.4, 37.6, 38.1, 37.7, 36.3, 38.7, 39.4, 38.8, 39.2, 40.3, 60, 58.3, 59.6, 59.1, 56.3, 55, 52.9, 54.1, 56.9, 56, 87, 92.7, 90.5, 85.8, 87.5, 88.3, 91.6, 88.2, 88.6, 84.7, 128, 130, 131, 129, 127, 129, 132, 133, 134, 133, 199, 204, 199, 207, 200, 200, 205, 202, 199, 199, 298, 298, 297, 288, 296, 293, 301, 299, 298, 293, 423, 421, 422, 428, 436, 427, 426, 428, 427, 429)), .Names = c("density", "gain"), class = "data.frame", row.names = c("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90" ))