Weekly retail sales achieved gains on both a year-over-year and sequential basis for the fourth week in a row, but department and specialty stores missed out on the holiday fireworks.

According to The Retail Economist-Goldman Sachs Weekly Chain Stores Sales Index, sales for the seven days ended July 4 were up 2.1 percent from the prior week, when they rose 2.2 percent and 3 percent above the comparable week in 2014.

The index, set at 100 in 1977, topped the 600 mark for the first time in its history, landing at 601.5.

Michael Niemira, chief economist and principal of The Retail Economist LLC, called the four-week positive streak “a very encouraging sign,” with housing-related spending remaining strong and improvements in online-only, discount, drug, dollar and office-supply retailers.

“But business in other retail segments seemingly runs in spurts with discounters, drug stores and dollar stores helping to lift spending over the past week, a period which included the Independence Day holiday,” he said.

Among the retailers with softer sales last week were department, apparel, grocery and electronics stores and wholesale clubs.

Department and apparel store activity will be watched closely as the summer progresses, with early reads on back-to-school and early fall subjects of greater attention.

Weather didn’t greatly affect last week’s retail results. According to Weather Trends International, the average temperature was 0.3 degrees cooler than last year but 0.2 degrees above its long-term average.

The U.S. Energy Information Administration reported that gas prices at the pump fell for a third consecutive week, descending 0.8 cents to $2.793 for a gallon of unleaded regular, 24.1 percent lower than one year ago.