If Rosh Chodesh Adar falls on Shabbos, they read the section of Shekalim (Exodus 30:11); if it falls on any other day, Shekalim is read on the previous Shabbos and there is no additional reading on the following Shabbos. On the second Shabbos, the section of Zachor (Deut. 15) is read; on the third Shabbos, they read the section of the red heifer, i.e., Parah (Numbers 19); on the fourth Shabbos, they read the section of HaChodesh (Exodus 17); on the fifth Shabbos, they resume the regular order of things. The normal order is also interrupted for Rosh Chodesh, Chanukah, Purim, fast days, maamados (see Taanis chapter 4) and Yom Kippur.
On Passover, they read the section about holidays in Leviticus (chapter 23); on Shavuos, they read “Seven weeks…” (Deut. 16); on Rosh Hashana, “In the seventh month, on the first day of the month…” (Lev. 23); on Yom Kippur, they read “After the death of Aaron’s sons…” (Lev. 16). On the first day of Succos, they read the section about holidays in Leviticus (chapter 23 again) and on the other days of Succos they read about the holiday’s offerings (Numbers 29).